- Ներածություն
- Փոփոխականներ
- Ֆունկցիաներ
- Օբյեկտներ և տվյալների ստրուկտուրաներ
- Կասներ
- SOLID
- Տեստավորում
- Concurrency
- Սխալների մշակում
- Ֆորմատավորում
- Մեկնաբանություններ
- Թարգմանություններ
Software engineering principles, from Robert C. Martin's book Clean Code, adapted for JavaScript. This is not a style guide. It's a guide to producing readable, reusable, and refactorable software in JavaScript.
Not every principle herein has to be strictly followed, and even fewer will be universally agreed upon. These are guidelines and nothing more, but they are ones codified over many years of collective experience by the authors of Clean Code.
Our craft of software engineering is just a bit over 50 years old, and we are still learning a lot. When software architecture is as old as architecture itself, maybe then we will have harder rules to follow. For now, let these guidelines serve as a touchstone by which to assess the quality of the JavaScript code that you and your team produce.
One more thing: knowing these won't immediately make you a better software developer, and working with them for many years doesn't mean you won't make mistakes. Every piece of code starts as a first draft, like wet clay getting shaped into its final form. Finally, we chisel away the imperfections when we review it with our peers. Don't beat yourself up for first drafts that need improvement. Beat up the code instead!
Վատ:
const yyyymmdstr = moment().format('YYYY/MM/DD');Լավ:
const currentDate = moment().format('YYYY/MM/DD');Վատ՝
getUserInfo();
getClientData();
getCustomerRecord();Լավ՝
getUser();Մենք պիտի ավելի շատ կոդ կարդանք, քան գրենք։ Կարևոր է մեր կոդը այնպես գրել, որ այն լինի ընթեռնելի և որոնելի։ Ծրագրում փոփոխականների լավ անունները կօգնեն հասկանալ ծրագրի նշանակությունը այն մարդկանց, ովքեր կցանկանան ուսումնասիրել քո ծրագրիը։ Փոփոխականների անունները որոնելի գրիր։ Հետևյալ գործիքները՝ buddy.js, ESLint կօգնեն հայտնաբերել չանվանված հաստատունները։
Վատ՝
// Ինչ թիվ է 86400000֊ը?
setTimeout(blastOff, 86400000);Լավ՝
// Հայտարարիր դրանք որպես հաստատուններ
const MILLISECONDS_IN_A_DAY = 86400000;
setTimeout(blastOff, MILLISECONDS_IN_A_DAY);Վատ՝
const address = 'One Infinite Loop, Cupertino 95014';
const cityZipCodeRegex = /^[^,\\]+[,\\\s]+(.+?)\s*(\d{5})?$/;
saveCityZipCode(address.match(cityZipCodeRegex)[1], address.match(cityZipCodeRegex)[2]);Լավ՝
const address = 'One Infinite Loop, Cupertino 95014';
const cityZipCodeRegex = /^[^,\\]+[,\\\s]+(.+?)\s*(\d{5})?$/;
const [, city, zipCode] = address.match(cityZipCodeRegex) || [];
saveCityZipCode(city, zipCode);Բացահայտը ավելի է քան թաքնվածը։
Վատ՝
const locations = ['Austin', 'New York', 'San Francisco'];
locations.forEach((l) => {
doStuff();
doSomeOtherStuff();
// ...
// ...
// ...
// սպասիր, ի՞նչ է l-ը
dispatch(l);
});Լավ՝
const locations = ['Austin', 'New York', 'San Francisco'];
locations.forEach((___location) => {
doStuff();
doSomeOtherStuff();
// ...
// ...
// ...
dispatch(___location);
});Եթե քո կլասը/օբյեկտը քեզ որևէ բան է ասում, մի կրկնիր նույնը փոփոխականների անուններում։
Վատ՝
const Car = {
carMake: 'Honda',
carModel: 'Accord',
carColor: 'Blue'
};
function paintCar(car) {
car.carColor = 'Red';
}Լավ՝
const Car = {
make: 'Honda',
model: 'Accord',
color: 'Blue'
};
function paintCar(car) {
car.color = 'Red';
}Սկզբնարժեքավորված արգումենտները հաճախ ավելի հասկանալի են քան մյուս տարբերակները կարճ արժեքավորումը։ Նաև
Իմացիր, որ եթե կարճ արժեքավորում օգտագործես, ապա քո ֆունկցիան կտրամադրի լռությամբ արժեքներ միայն արգումենտի undefined արժեքի դեպքում։
Արգումենտների այլ "կեղծոտ" արժեքները, ինչպիսիք են '', "", false, null, 0, և
NaN , չեն փոխարինվի լռությամբ արժեքներով։
Վատ՝
function createMicrobrewery(name) {
const breweryName = name || 'Hipster Brew Co.';
// ...
}Լավ՝
function createMicrobrewery(name = 'Hipster Brew Co.') {
// ...
}Ֆունկցիայի արգումենտների քանակը սահմանափակելը շատ կարևոր է, որովհետև դա հեշտացնում է ֆունկցիայի աշխատանքի տեստավորումը։ Երեքից ավել արգումենտներ ունենալը բերում է այն տարբերակների բազմացմանը , որոնք պետք է ստուգել յուրաքանչյուր արգումենտի հետ։
Մեկ կամ երկու արգումենտ ունենալը իդեալական է իսկ երեք արգումենտից հնարավորության դեպքում պետք է խուսափել։ Դրանցից ավելը պետք է խմբավորել։ Հաճախակի, եթե ունես երկու արգումենտից ավել, դա նշանակում է, որ ֆունկցիադ հավանաբար ավելի շատ բան է անում, քան անհրաժեշտ է։ Եթե ոչ, ապա օբյեկտը որպես արգումենտ փոխանցելը ավելի ճիշտ տարբերակ է։
Քանի որ, JavaScript֊ը թույլատրում է ընթացքից օբյեկտներ ստեղծել (առանց նախապես class-ով նախագծելու), կարող ես օգտագործել օբյեկտ եթե ունես շատ արգումենտների կարիք։
Ֆունկցիայի պահանջած հատկանիշները ակնհայտ սարքելու համար, կարող ես օգտագործել ES2015/ES6֊ից դեստրուկտուրիզացիայի սինտաքսը (destructuring syntax) , այն ունի որոշակի առավելություններ՝
-
Երբ մեկը նայում է ֆունկցիայի սիգնատուրային , միանգամից ակնհայտ է դառնում թե ինչ արգումենտներ են օգտագործվում
-
Դեստրուկտուրիզացիան կլոնավորում է ֆունկցիային փոխանցված արգումենտի պրիմիտիվ արժեքները։ Սա օգնում է խուսափել կողմնակի էֆեկտներից։ ՀԻՇԻՐ։ Դեստրուկտուրացված արժեքների օբյեկտները և զանգվածները չէն կլոնավորվում։
-
Լինթերները կարող են նախազգուշացնել չօգտագործված հատկանիշների մասին, ինչը անհնար կլինի առանց դեստրուկտուրիզացիայի։
Վատ՝
function createMenu(title, body, buttonText, cancellable) {
// ...
}Լավ՝
function createMenu({ title, body, buttonText, cancellable }) {
// ...
}
createMenu({
title: 'Foo',
body: 'Bar',
buttonText: 'Baz',
cancellable: true
});Սա ԾԱ նախագծման կարևորագույն սկզբունքն է։ Մեկից ավելի բան անող ֆունկցիաները դժվար են նախագծվում, տեստավորվում և նաև դրանց մասին մտածելը նույնպես դժվարանում է։ Եթե կարող ես յուրաքանչյուր գործողություն իզոլացնել մեկ ֆունկցիայի ներսում, ապա այդ ֆունկցիաները հեշտ փոփոխելի (refactoring) են դառնում և քո ծրագիրը ավելի հեշտ է կարդացվում։ Եթե այս ուղեցույցից վերցնես միայն այս կանոնը, դու արդեն առաջ կանցնես բազմաթիվ ծրագրավորողներից։
Վատ՝
function emailClients(clients) {
clients.forEach((client) => {
const clientRecord = database.lookup(client);
if (clientRecord.isActive()) {
email(client);
}
});
}Լավ՝
function emailActiveClients(clients) {
clients
.filter(isActiveClient)
.forEach(email);
}
function isActiveClient(client) {
const clientRecord = database.lookup(client);
return clientRecord.isActive();
}Վատ՝
function addToDate(date, month) {
// ...
}
const date = new Date();
// Դժվար է ֆունկցիայի անունից հասկանալ , թե ինչ է այն ավելացնում, օ՞ր, ամի՞ս, ի՜՞նչ ․․․
addToDate(date, 1);Լավ՝
function addMonthToDate(month, date) {
// ...
}
const date = new Date();
addMonthToDate(1, date);Աբստրակցիայի մեկ մակարդակից ավելին ունեցող ֆունկցիան, հավանաբար, անում է ավելին քան պետք է։ Ֆունկցիան բաժանելը մի քանի ֆունկցիաների օգնում է ֆունկցիաների վերաօգտագործելիությանը և հեշտ տեստավորմանը։
Վատ՝
function parseBetterJSAlternative(code) {
const REGEXES = [
// ...
];
const statements = code.split(' ');
const tokens = [];
REGEXES.forEach((REGEX) => {
statements.forEach((statement) => {
// ...
});
});
const ast = [];
tokens.forEach((token) => {
// lex...
});
ast.forEach((node) => {
// parse...
});
}Լավ՝
function parseBetterJSAlternative(code) {
const tokens = tokenize(code);
const ast = lexer(tokens);
ast.forEach((node) => {
// parse...
});
}
function tokenize(code) {
const REGEXES = [
// ...
];
const statements = code.split(' ');
const tokens = [];
REGEXES.forEach((REGEX) => {
statements.forEach((statement) => {
tokens.push( /* ... */ );
});
});
return tokens;
}
function lexer(tokens) {
const ast = [];
tokens.forEach((token) => {
ast.push( /* ... */ );
});
return ast;
}Do your absolute best to avoid duplicate code. Duplicate code is bad because it means that there's more than one place to alter something if you need to change some logic.
Imagine if you run a restaurant and you keep track of your inventory: all your tomatoes, onions, garlic, spices, etc. If you have multiple lists that you keep this on, then all have to be updated when you serve a dish with tomatoes in them. If you only have one list, there's only one place to update!
Oftentimes you have duplicate code because you have two or more slightly different things, that share a lot in common, but their differences force you to have two or more separate functions that do much of the same things. Removing duplicate code means creating an abstraction that can handle this set of different things with just one function/module/class.
Getting the abstraction right is critical, that's why you should follow the SOLID principles laid out in the Classes section. Bad abstractions can be worse than duplicate code, so be careful! Having said this, if you can make a good abstraction, do it! Don't repeat yourself, otherwise you'll find yourself updating multiple places anytime you want to change one thing.
Վատ՝
function showDeveloperList(developers) {
developers.forEach((developer) => {
const expectedSalary = developer.calculateExpectedSalary();
const experience = developer.getExperience();
const githubLink = developer.getGithubLink();
const data = {
expectedSalary,
experience,
githubLink
};
render(data);
});
}
function showManagerList(managers) {
managers.forEach((manager) => {
const expectedSalary = manager.calculateExpectedSalary();
const experience = manager.getExperience();
const portfolio = manager.getMBAProjects();
const data = {
expectedSalary,
experience,
portfolio
};
render(data);
});
}Լավ՝
function showEmployeeList(employees) {
employees.forEach((employee) => {
const expectedSalary = employee.calculateExpectedSalary();
const experience = employee.getExperience();
const data = {
expectedSalary,
experience
};
switch (employee.type) {
case 'manager':
data.portfolio = employee.getMBAProjects();
break;
case 'developer':
data.githubLink = employee.getGithubLink();
break;
}
render(data);
});
}Վատ՝
const menuConfig = {
title: null,
body: 'Bar',
buttonText: null,
cancellable: true
};
function createMenu(config) {
config.title = config.title || 'Foo';
config.body = config.body || 'Bar';
config.buttonText = config.buttonText || 'Baz';
config.cancellable = config.cancellable !== undefined ? config.cancellable : true;
}
createMenu(menuConfig);Լավ՝
const menuConfig = {
title: 'Order',
// User did not include 'body' key
buttonText: 'Send',
cancellable: true
};
function createMenu(config) {
config = Object.assign({
title: 'Foo',
body: 'Bar',
buttonText: 'Baz',
cancellable: true
}, config);
// config now equals: {title: "Order", body: "Bar", buttonText: "Send", cancellable: true}
// ...
}
createMenu(menuConfig);Տրամաբանական փոփոխականը որպես արգումենտ, օգտագործողին հուշում է, որ ձեր ֆունկցիան մեկից ավելի բաներ է անում։ Բայց լավ ֆունկցիան պետք է կատարի միայն մեկ բան։ Նման ֆունկցիաները կարող եք բաժանել երկու մասի։
Վատ՝
function createFile(name, temp) {
if (temp) {
fs.create(`./temp/${name}`);
} else {
fs.create(name);
}
}Լավ՝
function createFile(name) {
fs.create(name);
}
function createTempFile(name) {
createFile(`./temp/${name}`);
}Եթե ֆունկցիան բացի արգումենտ ստանալը և ինչ֊որ բան վերադարձնելը, անում է նաև այլ գործողություններ, ապար դա համարվում է կողմնակի ազդեցություն։ Կողմնակի ազդեցության օրինակներ են, ֆայլի մեջ գրելը, ինչ֊որ գլոբալ փոփոխական փոխելը, կամ պատահաբար ձեր հաշվի գումարը այլ մարդու փոխանցելը։
Հաճախ կարիք է լինում օգտագործել կողմնակի ազդեցություններ, ինչպիսիք են վերոշարադրյալները, քանի որ երբեմն պետք է գրել ֆայլի մեջ։ Նման դեպքերում դուք պետք է առանձնացնեք և կենտրոնացնեք ծրագրի այն մասերը որոնք ունեն կողմնակի ազդեցություն ու մի տեղից կատարել ֆայլիերի մանիպուլիացիան։ Մի ստեղծեք մի քանի ֆունկցիա միևնույն ֆայլի վրա գրելու համար։ Գրեք մեկ և միայն մեկ service (ծառայություն) որն անում է այդ գորոծղությունը։
Հիմնական իմաստն այն է, որ չստեղծեք ընդհանուր օգտագործման օբյեկտներ առանց դրա վրա կառուցելու ձևափոխությունների կենտրոնացված կլաս կամ օբյեկտ։ Քանի որ նման դեպքում, ծրագրի տարբեր մասերում կարող է ձևափոխվել ձեր օբյեկտը և դուք ստանաք անկանխատեսելի արդյունքներ։ Եթե կարողանաք խուսափել այս տարածված խնդիրց, ապա շատ ավելի երջանիկ կլինեք, քան ծրագրավորողների մեծ մասը։
Վատ՝
// Global variable referenced by following function.
// If we had another function that used this name, now it'd be an array and it could break it.
let name = 'Ryan McDermott';
function splitIntoFirstAndLastName() {
name = name.split(' ');
}
splitIntoFirstAndLastName();
console.log(name); // ['Ryan', 'McDermott'];Լավ՝
function splitIntoFirstAndLastName(name) {
return name.split(' ');
}
const name = 'Ryan McDermott';
const newName = splitIntoFirstAndLastName(name);
console.log(name); // 'Ryan McDermott';
console.log(newName); // ['Ryan', 'McDermott'];In JavaScript, primitives are passed by value and objects/arrays are passed by
reference. In the case of objects and arrays, if your function makes a change
in a shopping cart array, for example, by adding an item to purchase,
then any other function that uses that cart array will be affected by this
addition. That may be great, however it can be bad too. Let's imagine a bad
situation:
The user clicks the "Purchase", button which calls a purchase function that
spawns a network request and sends the cart array to the server. Because
of a bad network connection, the purchase function has to keep retrying the
request. Now, what if in the meantime the user accidentally clicks "Add to Cart"
button on an item they don't actually want before the network request begins?
If that happens and the network request begins, then that purchase function
will send the accidentally added item because it has a reference to a shopping
cart array that the addItemToCart function modified by adding an unwanted
item.
A great solution would be for the addItemToCart to always clone the cart,
edit it, and return the clone. This ensures that no other functions that are
holding onto a reference of the shopping cart will be affected by any changes.
Two caveats to mention to this approach:
-
There might be cases where you actually want to modify the input object, but when you adopt this programming practice you will find that those cases are pretty rare. Most things can be refactored to have no side effects!
-
Cloning big objects can be very expensive in terms of performance. Luckily, this isn't a big issue in practice because there are great libraries that allow this kind of programming approach to be fast and not as memory intensive as it would be for you to manually clone objects and arrays.
Վատ՝
const addItemToCart = (cart, item) => {
cart.push({ item, date: Date.now() });
};Լավ՝
const addItemToCart = (cart, item) => {
return [...cart, { item, date: Date.now() }];
};Polluting globals is a bad practice in JavaScript because you could clash with another
library and the user of your API would be none-the-wiser until they get an
exception in production. Let's think about an example: what if you wanted to
extend JavaScript's native Array method to have a diff method that could
show the difference between two arrays? You could write your new function
to the Array.prototype, but it could clash with another library that tried
to do the same thing. What if that other library was just using diff to find
the difference between the first and last elements of an array? This is why it
would be much better to just use ES2015/ES6 classes and simply extend the Array global.
Վատ՝
Array.prototype.diff = function diff(comparisonArray) {
const hash = new Set(comparisonArray);
return this.filter(elem => !hash.has(elem));
};Լավ՝
class SuperArray extends Array {
diff(comparisonArray) {
const hash = new Set(comparisonArray);
return this.filter(elem => !hash.has(elem));
}
}JavaScript isn't a functional language in the way that Haskell is, but it has a functional flavor to it. Functional languages can be cleaner and easier to test. Favor this style of programming when you can.
Վատ՝
const programmerOutput = [
{
name: 'Uncle Bobby',
linesOfCode: 500
}, {
name: 'Suzie Q',
linesOfCode: 1500
}, {
name: 'Jimmy Gosling',
linesOfCode: 150
}, {
name: 'Gracie Hopper',
linesOfCode: 1000
}
];
let totalOutput = 0;
for (let i = 0; i < programmerOutput.length; i++) {
totalOutput += programmerOutput[i].linesOfCode;
}Լավ՝
const programmerOutput = [
{
name: 'Uncle Bobby',
linesOfCode: 500
}, {
name: 'Suzie Q',
linesOfCode: 1500
}, {
name: 'Jimmy Gosling',
linesOfCode: 150
}, {
name: 'Gracie Hopper',
linesOfCode: 1000
}
];
const totalOutput = programmerOutput
.map(output => output.linesOfCode)
.reduce((totalLines, lines) => totalLines + lines);Վատ՝
if (fsm.state === 'fetching' && isEmpty(listNode)) {
// ...
}Լավ՝
function shouldShowSpinner(fsm, listNode) {
return fsm.state === 'fetching' && isEmpty(listNode);
}
if (shouldShowSpinner(fsmInstance, listNodeInstance)) {
// ...
}Վատ՝
function isDOMNodeNotPresent(node) {
// ...
}
if (!isDOMNodeNotPresent(node)) {
// ...
}Լավ՝
function isDOMNodePresent(node) {
// ...
}
if (isDOMNodePresent(node)) {
// ...
}This seems like an impossible task. Upon first hearing this, most people say,
"how am I supposed to do anything without an if statement?" The answer is that
you can use polymorphism to achieve the same task in many cases. The second
question is usually, "well that's great but why would I want to do that?" The
answer is a previous clean code concept we learned: a function should only do
one thing. When you have classes and functions that have if statements, you
are telling your user that your function does more than one thing. Remember,
just do one thing.
Վատ՝
class Airplane {
// ...
getCruisingAltitude() {
switch (this.type) {
case '777':
return this.getMaxAltitude() - this.getPassengerCount();
case 'Air Force One':
return this.getMaxAltitude();
case 'Cessna':
return this.getMaxAltitude() - this.getFuelExpenditure();
}
}
}Լավ՝
class Airplane {
// ...
}
class Boeing777 extends Airplane {
// ...
getCruisingAltitude() {
return this.getMaxAltitude() - this.getPassengerCount();
}
}
class AirForceOne extends Airplane {
// ...
getCruisingAltitude() {
return this.getMaxAltitude();
}
}
class Cessna extends Airplane {
// ...
getCruisingAltitude() {
return this.getMaxAltitude() - this.getFuelExpenditure();
}
}JavaScript is untyped, which means your functions can take any type of argument. Sometimes you are bitten by this freedom and it becomes tempting to do type-checking in your functions. There are many ways to avoid having to do this. The first thing to consider is consistent APIs.
Վատ՝
function travelToTexas(vehicle) {
if (vehicle instanceof Bicycle) {
vehicle.pedal(this.currentLocation, new Location('texas'));
} else if (vehicle instanceof Car) {
vehicle.drive(this.currentLocation, new Location('texas'));
}
}Լավ՝
function travelToTexas(vehicle) {
vehicle.move(this.currentLocation, new Location('texas'));
}If you are working with basic primitive values like strings and integers, and you can't use polymorphism but you still feel the need to type-check, you should consider using TypeScript. It is an excellent alternative to normal JavaScript, as it provides you with static typing on top of standard JavaScript syntax. The problem with manually type-checking normal JavaScript is that doing it well requires so much extra verbiage that the faux "type-safety" you get doesn't make up for the lost readability. Keep your JavaScript clean, write good tests, and have good code reviews. Otherwise, do all of that but with TypeScript (which, like I said, is a great alternative!).
Վատ՝
function combine(val1, val2) {
if (typeof val1 === 'number' && typeof val2 === 'number' ||
typeof val1 === 'string' && typeof val2 === 'string') {
return val1 + val2;
}
throw new Error('Must be of type String or Number');
}Լավ՝
function combine(val1, val2) {
return val1 + val2;
}Modern browsers do a lot of optimization under-the-hood at runtime. A lot of times, if you are optimizing then you are just wasting your time. There are good resources for seeing where optimization is lacking. Target those in the meantime, until they are fixed if they can be.
Վատ՝
// On old browsers, each iteration with uncached `list.length` would be costly
// because of `list.length` recomputation. In modern browsers, this is optimized.
for (let i = 0, len = list.length; i < len; i++) {
// ...
}Լավ՝
for (let i = 0; i < list.length; i++) {
// ...
}Dead code is just as bad as duplicate code. There's no reason to keep it in your codebase. If it's not being called, get rid of it! It will still be safe in your version history if you still need it.
Վատ՝
function oldRequestModule(url) {
// ...
}
function newRequestModule(url) {
// ...
}
const req = newRequestModule;
inventoryTracker('apples', req, 'www.inventory-awesome.io');Լավ՝
function newRequestModule(url) {
// ...
}
const req = newRequestModule;
inventoryTracker('apples', req, 'www.inventory-awesome.io');Using getters and setters to access data on objects could be better than simply looking for a property on an object. "Why?" you might ask. Well, here's an unorganized list of reasons why:
- When you want to do more beyond getting an object property, you don't have to look up and change every accessor in your codebase.
- Makes adding validation simple when doing a
set. - Encapsulates the internal representation.
- Easy to add logging and error handling when getting and setting.
- You can lazy load your object's properties, let's say getting it from a server.
Վատ՝
function makeBankAccount() {
// ...
return {
balance: 0,
// ...
};
}
const account = makeBankAccount();
account.balance = 100;Լավ՝
function makeBankAccount() {
// this one is private
let balance = 0;
// a "getter", made public via the returned object below
function getBalance() {
return balance;
}
// a "setter", made public via the returned object below
function setBalance(amount) {
// ... validate before updating the balance
balance = amount;
}
return {
// ...
getBalance,
setBalance,
};
}
const account = makeBankAccount();
account.setBalance(100);This can be accomplished through closures (for ES5 and below).
Վատ՝
const Employee = function(name) {
this.name = name;
};
Employee.prototype.getName = function getName() {
return this.name;
};
const employee = new Employee('John Doe');
console.log(`Employee name: ${employee.getName()}`); // Employee name: John Doe
delete employee.name;
console.log(`Employee name: ${employee.getName()}`); // Employee name: undefinedԼավ՝
function makeEmployee(name) {
return {
getName() {
return name;
},
};
}
const employee = makeEmployee('John Doe');
console.log(`Employee name: ${employee.getName()}`); // Employee name: John Doe
delete employee.name;
console.log(`Employee name: ${employee.getName()}`); // Employee name: John DoeIt's very difficult to get readable class inheritance, construction, and method definitions for classical ES5 classes. If you need inheritance (and be aware that you might not), then prefer ES2015/ES6 classes. However, prefer small functions over classes until you find yourself needing larger and more complex objects.
Վատ՝
const Animal = function(age) {
if (!(this instanceof Animal)) {
throw new Error('Instantiate Animal with `new`');
}
this.age = age;
};
Animal.prototype.move = function move() {};
const Mammal = function(age, furColor) {
if (!(this instanceof Mammal)) {
throw new Error('Instantiate Mammal with `new`');
}
Animal.call(this, age);
this.furColor = furColor;
};
Mammal.prototype = Object.create(Animal.prototype);
Mammal.prototype.constructor = Mammal;
Mammal.prototype.liveBirth = function liveBirth() {};
const Human = function(age, furColor, languageSpoken) {
if (!(this instanceof Human)) {
throw new Error('Instantiate Human with `new`');
}
Mammal.call(this, age, furColor);
this.languageSpoken = languageSpoken;
};
Human.prototype = Object.create(Mammal.prototype);
Human.prototype.constructor = Human;
Human.prototype.speak = function speak() {};Լավ՝
class Animal {
constructor(age) {
this.age = age;
}
move() { /* ... */ }
}
class Mammal extends Animal {
constructor(age, furColor) {
super(age);
this.furColor = furColor;
}
liveBirth() { /* ... */ }
}
class Human extends Mammal {
constructor(age, furColor, languageSpoken) {
super(age, furColor);
this.languageSpoken = languageSpoken;
}
speak() { /* ... */ }
}This pattern is very useful in JavaScript and you see it in many libraries such
as jQuery and Lodash. It allows your code to be expressive, and less verbose.
For that reason, I say, use method chaining and take a look at how clean your code
will be. In your class functions, simply return this at the end of every function,
and you can chain further class methods onto it.
Վատ՝
class Car {
constructor(make, model, color) {
this.make = make;
this.model = model;
this.color = color;
}
setMake(make) {
this.make = make;
}
setModel(model) {
this.model = model;
}
setColor(color) {
this.color = color;
}
save() {
console.log(this.make, this.model, this.color);
}
}
const car = new Car('Ford','F-150','red');
car.setColor('pink');
car.save();Լավ՝
class Car {
constructor(make, model, color) {
this.make = make;
this.model = model;
this.color = color;
}
setMake(make) {
this.make = make;
// NOTE: Returning this for chaining
return this;
}
setModel(model) {
this.model = model;
// NOTE: Returning this for chaining
return this;
}
setColor(color) {
this.color = color;
// NOTE: Returning this for chaining
return this;
}
save() {
console.log(this.make, this.model, this.color);
// NOTE: Returning this for chaining
return this;
}
}
const car = new Car('Ford','F-150','red')
.setColor('pink')
.save();As stated famously in Design Patterns by the Gang of Four, you should prefer composition over inheritance where you can. There are lots of good reasons to use inheritance and lots of good reasons to use composition. The main point for this maxim is that if your mind instinctively goes for inheritance, try to think if composition could model your problem better. In some cases it can.
You might be wondering then, "when should I use inheritance?" It depends on your problem at hand, but this is a decent list of when inheritance makes more sense than composition:
- Your inheritance represents an "is-a" relationship and not a "has-a" relationship (Human->Animal vs. User->UserDetails).
- You can reuse code from the base classes (Humans can move like all animals).
- You want to make global changes to derived classes by changing a base class. (Change the caloric expenditure of all animals when they move).
Վատ՝
class Employee {
constructor(name, email) {
this.name = name;
this.email = email;
}
// ...
}
// Bad because Employees "have" tax data. EmployeeTaxData is not a type of Employee
class EmployeeTaxData extends Employee {
constructor(ssn, salary) {
super();
this.ssn = ssn;
this.salary = salary;
}
// ...
}Լավ՝
class EmployeeTaxData {
constructor(ssn, salary) {
this.ssn = ssn;
this.salary = salary;
}
// ...
}
class Employee {
constructor(name, email) {
this.name = name;
this.email = email;
}
setTaxData(ssn, salary) {
this.taxData = new EmployeeTaxData(ssn, salary);
}
// ...
}As stated in Clean Code, "There should never be more than one reason for a class to change". It's tempting to jam-pack a class with a lot of functionality, like when you can only take one suitcase on your flight. The issue with this is that your class won't be conceptually cohesive and it will give it many reasons to change. Minimizing the amount of times you need to change a class is important. It's important because if too much functionality is in one class and you modify a piece of it, it can be difficult to understand how that will affect other dependent modules in your codebase.
Վատ՝
class UserSettings {
constructor(user) {
this.user = user;
}
changeSettings(settings) {
if (this.verifyCredentials()) {
// ...
}
}
verifyCredentials() {
// ...
}
}Լավ՝
class UserAuth {
constructor(user) {
this.user = user;
}
verifyCredentials() {
// ...
}
}
class UserSettings {
constructor(user) {
this.user = user;
this.auth = new UserAuth(user);
}
changeSettings(settings) {
if (this.auth.verifyCredentials()) {
// ...
}
}
}As stated by Bertrand Meyer, "software entities (classes, modules, functions, etc.) should be open for extension, but closed for modification." What does that mean though? This principle basically states that you should allow users to add new functionalities without changing existing code.
Վատ՝
class AjaxAdapter extends Adapter {
constructor() {
super();
this.name = 'ajaxAdapter';
}
}
class NodeAdapter extends Adapter {
constructor() {
super();
this.name = 'nodeAdapter';
}
}
class HttpRequester {
constructor(adapter) {
this.adapter = adapter;
}
fetch(url) {
if (this.adapter.name === 'ajaxAdapter') {
return makeAjaxCall(url).then((response) => {
// transform response and return
});
} else if (this.adapter.name === 'httpNodeAdapter') {
return makeHttpCall(url).then((response) => {
// transform response and return
});
}
}
}
function makeAjaxCall(url) {
// request and return promise
}
function makeHttpCall(url) {
// request and return promise
}Լավ՝
class AjaxAdapter extends Adapter {
constructor() {
super();
this.name = 'ajaxAdapter';
}
request(url) {
// request and return promise
}
}
class NodeAdapter extends Adapter {
constructor() {
super();
this.name = 'nodeAdapter';
}
request(url) {
// request and return promise
}
}
class HttpRequester {
constructor(adapter) {
this.adapter = adapter;
}
fetch(url) {
return this.adapter.request(url).then((response) => {
// transform response and return
});
}
}This is a scary term for a very simple concept. It's formally defined as "If S is a subtype of T, then objects of type T may be replaced with objects of type S (i.e., objects of type S may substitute objects of type T) without altering any of the desirable properties of that program (correctness, task performed, etc.)." That's an even scarier definition.
The best explanation for this is if you have a parent class and a child class, then the base class and child class can be used interchangeably without getting incorrect results. This might still be confusing, so let's take a look at the classic Square-Rectangle example. Mathematically, a square is a rectangle, but if you model it using the "is-a" relationship via inheritance, you quickly get into trouble.
Վատ՝
class Rectangle {
constructor() {
this.width = 0;
this.height = 0;
}
setColor(color) {
// ...
}
render(area) {
// ...
}
setWidth(width) {
this.width = width;
}
setHeight(height) {
this.height = height;
}
getArea() {
return this.width * this.height;
}
}
class Square extends Rectangle {
setWidth(width) {
this.width = width;
this.height = width;
}
setHeight(height) {
this.width = height;
this.height = height;
}
}
function renderLargeRectangles(rectangles) {
rectangles.forEach((rectangle) => {
rectangle.setWidth(4);
rectangle.setHeight(5);
const area = rectangle.getArea(); // BAD: Returns 25 for Square. Should be 20.
rectangle.render(area);
});
}
const rectangles = [new Rectangle(), new Rectangle(), new Square()];
renderLargeRectangles(rectangles);Լավ՝
class Shape {
setColor(color) {
// ...
}
render(area) {
// ...
}
}
class Rectangle extends Shape {
constructor(width, height) {
super();
this.width = width;
this.height = height;
}
getArea() {
return this.width * this.height;
}
}
class Square extends Shape {
constructor(length) {
super();
this.length = length;
}
getArea() {
return this.length * this.length;
}
}
function renderLargeShapes(shapes) {
shapes.forEach((shape) => {
const area = shape.getArea();
shape.render(area);
});
}
const shapes = [new Rectangle(4, 5), new Rectangle(4, 5), new Square(5)];
renderLargeShapes(shapes);JavaScript doesn't have interfaces so this principle doesn't apply as strictly as others. However, it's important and relevant even with JavaScript's lack of type system.
ISP states that "Clients should not be forced to depend upon interfaces that they do not use." Interfaces are implicit contracts in JavaScript because of duck typing.
A good example to look at that demonstrates this principle in JavaScript is for classes that require large settings objects. Not requiring clients to setup huge amounts of options is beneficial, because most of the time they won't need all of the settings. Making them optional helps prevent having a "fat interface".
Վատ՝
class DOMTraverser {
constructor(settings) {
this.settings = settings;
this.setup();
}
setup() {
this.rootNode = this.settings.rootNode;
this.animationModule.setup();
}
traverse() {
// ...
}
}
const $ = new DOMTraverser({
rootNode: document.getElementsByTagName('body'),
animationModule() {} // Most of the time, we won't need to animate when traversing.
// ...
});Լավ՝
class DOMTraverser {
constructor(settings) {
this.settings = settings;
this.options = settings.options;
this.setup();
}
setup() {
this.rootNode = this.settings.rootNode;
this.setupOptions();
}
setupOptions() {
if (this.options.animationModule) {
// ...
}
}
traverse() {
// ...
}
}
const $ = new DOMTraverser({
rootNode: document.getElementsByTagName('body'),
options: {
animationModule() {}
}
});This principle states two essential things:
- High-level modules should not depend on low-level modules. Both should depend on abstractions.
- Abstractions should not depend upon details. Details should depend on abstractions.
This can be hard to understand at first, but if you've worked with AngularJS, you've seen an implementation of this principle in the form of Dependency Injection (DI). While they are not identical concepts, DIP keeps high-level modules from knowing the details of its low-level modules and setting them up. It can accomplish this through DI. A huge benefit of this is that it reduces the coupling between modules. Coupling is a very bad development pattern because it makes your code hard to refactor.
As stated previously, JavaScript doesn't have interfaces so the abstractions
that are depended upon are implicit contracts. That is to say, the methods
and properties that an object/class exposes to another object/class. In the
example below, the implicit contract is that any Request module for an
InventoryTracker will have a requestItems method.
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class InventoryRequester {
constructor() {
this.REQ_METHODS = ['HTTP'];
}
requestItem(item) {
// ...
}
}
class InventoryTracker {
constructor(items) {
this.items = items;
// BAD: We have created a dependency on a specific request implementation.
// We should just have requestItems depend on a request method: `request`
this.requester = new InventoryRequester();
}
requestItems() {
this.items.forEach((item) => {
this.requester.requestItem(item);
});
}
}
const inventoryTracker = new InventoryTracker(['apples', 'bananas']);
inventoryTracker.requestItems();Լավ՝
class InventoryTracker {
constructor(items, requester) {
this.items = items;
this.requester = requester;
}
requestItems() {
this.items.forEach((item) => {
this.requester.requestItem(item);
});
}
}
class InventoryRequesterV1 {
constructor() {
this.REQ_METHODS = ['HTTP'];
}
requestItem(item) {
// ...
}
}
class InventoryRequesterV2 {
constructor() {
this.REQ_METHODS = ['WS'];
}
requestItem(item) {
// ...
}
}
// By constructing our dependencies externally and injecting them, we can easily
// substitute our request module for a fancy new one that uses WebSockets.
const inventoryTracker = new InventoryTracker(['apples', 'bananas'], new InventoryRequesterV2());
inventoryTracker.requestItems();Testing is more important than shipping. If you have no tests or an inadequate amount, then every time you ship code you won't be sure that you didn't break anything. Deciding on what constitutes an adequate amount is up to your team, but having 100% coverage (all statements and branches) is how you achieve very high confidence and developer peace of mind. This means that in addition to having a great testing framework, you also need to use a good coverage tool.
There's no excuse to not write tests. There are plenty of good JS test frameworks, so find one that your team prefers. When you find one that works for your team, then aim to always write tests for every new feature/module you introduce. If your preferred method is Test Driven Development (TDD), that is great, but the main point is to just make sure you are reaching your coverage goals before launching any feature, or refactoring an existing one.
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import assert from 'assert';
describe('MakeMomentJSGreatAgain', () => {
it('handles date boundaries', () => {
let date;
date = new MakeMomentJSGreatAgain('1/1/2015');
date.addDays(30);
assert.equal('1/31/2015', date);
date = new MakeMomentJSGreatAgain('2/1/2016');
date.addDays(28);
assert.equal('02/29/2016', date);
date = new MakeMomentJSGreatAgain('2/1/2015');
date.addDays(28);
assert.equal('03/01/2015', date);
});
});Լավ՝
import assert from 'assert';
describe('MakeMomentJSGreatAgain', () => {
it('handles 30-day months', () => {
const date = new MakeMomentJSGreatAgain('1/1/2015');
date.addDays(30);
assert.equal('1/31/2015', date);
});
it('handles leap year', () => {
const date = new MakeMomentJSGreatAgain('2/1/2016');
date.addDays(28);
assert.equal('02/29/2016', date);
});
it('handles non-leap year', () => {
const date = new MakeMomentJSGreatAgain('2/1/2015');
date.addDays(28);
assert.equal('03/01/2015', date);
});
});Callbacks aren't clean, and they cause excessive amounts of nesting. With ES2015/ES6, Promises are a built-in global type. Use them!
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import { get } from 'request';
import { writeFile } from 'fs';
get('https://en.wikipedia.org/wiki/Robert_Cecil_Martin', (requestErr, response) => {
if (requestErr) {
console.error(requestErr);
} else {
writeFile('article.html', response.body, (writeErr) => {
if (writeErr) {
console.error(writeErr);
} else {
console.log('File written');
}
});
}
});Լավ՝
import { get } from 'request';
import { writeFile } from 'fs';
get('https://en.wikipedia.org/wiki/Robert_Cecil_Martin')
.then((response) => {
return writeFile('article.html', response);
})
.then(() => {
console.log('File written');
})
.catch((err) => {
console.error(err);
});Promises are a very clean alternative to callbacks, but ES2017/ES8 brings async and await
which offer an even cleaner solution. All you need is a function that is prefixed
in an async keyword, and then you can write your logic imperatively without
a then chain of functions. Use this if you can take advantage of ES2017/ES8 features
today!
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import { get } from 'request-promise';
import { writeFile } from 'fs-promise';
get('https://en.wikipedia.org/wiki/Robert_Cecil_Martin')
.then((response) => {
return writeFile('article.html', response);
})
.then(() => {
console.log('File written');
})
.catch((err) => {
console.error(err);
});Լավ՝
import { get } from 'request-promise';
import { writeFile } from 'fs-promise';
async function getCleanCodeArticle() {
try {
const response = await get('https://en.wikipedia.org/wiki/Robert_Cecil_Martin');
await writeFile('article.html', response);
console.log('File written');
} catch(err) {
console.error(err);
}
}Thrown errors are a good thing! They mean the runtime has successfully identified when something in your program has gone wrong and it's letting you know by stopping function execution on the current stack, killing the process (in Node), and notifying you in the console with a stack trace.
Doing nothing with a caught error doesn't give you the ability to ever fix
or react to said error. Logging the error to the console (console.log)
isn't much better as often times it can get lost in a sea of things printed
to the console. If you wrap any bit of code in a try/catch it means you
think an error may occur there and therefore you should have a plan,
or create a code path, for when it occurs.
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try {
functionThatMightThrow();
} catch (error) {
console.log(error);
}Լավ՝
try {
functionThatMightThrow();
} catch (error) {
// One option (more noisy than console.log):
console.error(error);
// Another option:
notifyUserOfError(error);
// Another option:
reportErrorToService(error);
// OR do all three!
}For the same reason you shouldn't ignore caught errors
from try/catch.
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getdata()
.then((data) => {
functionThatMightThrow(data);
})
.catch((error) => {
console.log(error);
});Լավ՝
getdata()
.then((data) => {
functionThatMightThrow(data);
})
.catch((error) => {
// One option (more noisy than console.log):
console.error(error);
// Another option:
notifyUserOfError(error);
// Another option:
reportErrorToService(error);
// OR do all three!
});Formatting is subjective. Like many rules herein, there is no hard and fast rule that you must follow. The main point is DO NOT ARGUE over formatting. There are tons of tools to automate this. Use one! It's a waste of time and money for engineers to argue over formatting.
For things that don't fall under the purview of automatic formatting (indentation, tabs vs. spaces, double vs. single quotes, etc.) look here for some guidance.
JavaScript is untyped, so capitalization tells you a lot about your variables, functions, etc. These rules are subjective, so your team can choose whatever they want. The point is, no matter what you all choose, just be consistent.
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const DAYS_IN_WEEK = 7;
const daysInMonth = 30;
const songs = ['Back In Black', 'Stairway to Heaven', 'Hey Jude'];
const Artists = ['ACDC', 'Led Zeppelin', 'The Beatles'];
function eraseDatabase() {}
function restore_database() {}
class animal {}
class Alpaca {}Լավ՝
const DAYS_IN_WEEK = 7;
const DAYS_IN_MONTH = 30;
const SONGS = ['Back In Black', 'Stairway to Heaven', 'Hey Jude'];
const ARTISTS = ['ACDC', 'Led Zeppelin', 'The Beatles'];
function eraseDatabase() {}
function restoreDatabase() {}
class Animal {}
class Alpaca {}If a function calls another, keep those functions vertically close in the source file. Ideally, keep the caller right above the callee. We tend to read code from top-to-bottom, like a newspaper. Because of this, make your code read that way.
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class PerformanceReview {
constructor(employee) {
this.employee = employee;
}
lookupPeers() {
return db.lookup(this.employee, 'peers');
}
lookupManager() {
return db.lookup(this.employee, 'manager');
}
getPeerReviews() {
const peers = this.lookupPeers();
// ...
}
perfReview() {
this.getPeerReviews();
this.getManagerReview();
this.getSelfReview();
}
getManagerReview() {
const manager = this.lookupManager();
}
getSelfReview() {
// ...
}
}
const review = new PerformanceReview(employee);
review.perfReview();Լավ՝
class PerformanceReview {
constructor(employee) {
this.employee = employee;
}
perfReview() {
this.getPeerReviews();
this.getManagerReview();
this.getSelfReview();
}
getPeerReviews() {
const peers = this.lookupPeers();
// ...
}
lookupPeers() {
return db.lookup(this.employee, 'peers');
}
getManagerReview() {
const manager = this.lookupManager();
}
lookupManager() {
return db.lookup(this.employee, 'manager');
}
getSelfReview() {
// ...
}
}
const review = new PerformanceReview(employee);
review.perfReview();Comments are an apology, not a requirement. Good code mostly documents itself.
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function hashIt(data) {
// The hash
let hash = 0;
// Length of string
const length = data.length;
// Loop through every character in data
for (let i = 0; i < length; i++) {
// Get character code.
const char = data.charCodeAt(i);
// Make the hash
hash = ((hash << 5) - hash) + char;
// Convert to 32-bit integer
hash &= hash;
}
}Լավ՝
function hashIt(data) {
let hash = 0;
const length = data.length;
for (let i = 0; i < length; i++) {
const char = data.charCodeAt(i);
hash = ((hash << 5) - hash) + char;
// Convert to 32-bit integer
hash &= hash;
}
}Version control exists for a reason. Leave old code in your history.
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doStuff();
// doOtherStuff();
// doSomeMoreStuff();
// doSoMuchStuff();Լավ՝
doStuff();Remember, use version control! There's no need for dead code, commented code,
and especially journal comments. Use git log to get history!
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/**
* 2016-12-20: Removed monads, didn't understand them (RM)
* 2016-10-01: Improved using special monads (JP)
* 2016-02-03: Removed type-checking (LI)
* 2015-03-14: Added combine with type-checking (JR)
*/
function combine(a, b) {
return a + b;
}Լավ՝
function combine(a, b) {
return a + b;
}They usually just add noise. Let the functions and variable names along with the proper indentation and formatting give the visual structure to your code.
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////////////////////////////////////////////////////////////////////////////////
// Scope Model Instantiation
////////////////////////////////////////////////////////////////////////////////
$scope.model = {
menu: 'foo',
nav: 'bar'
};
////////////////////////////////////////////////////////////////////////////////
// Action setup
////////////////////////////////////////////////////////////////////////////////
const actions = function() {
// ...
};Լավ՝
$scope.model = {
menu: 'foo',
nav: 'bar'
};
const actions = function() {
// ...
};This is also available in other languages:
Brazilian Portuguese: fesnt/clean-code-javascript
Spanish: andersontr15/clean-code-javascript
Chinese:
German: marcbruederlin/clean-code-javascript
Korean: qkraudghgh/clean-code-javascript-ko
Polish: greg-dev/clean-code-javascript-pl
Russian:
Vietnamese: hienvd/clean-code-javascript/
Japanese: mitsuruog/clean-code-javascript/
Indonesia:
andirkh/clean-code-javascript/