Add O(sqrt n) solution in JS

Author: stellarbeam

Is prime?/solution.js

@@ -0,0 +1,12 @@
+function isPrime(n) {
+    if(n<2) return false
+    let prime = true
+    for (let i = 2; i*i<= n; i++) {
+        if( n%i == 0) {
+            prime = false
+            break
+        }
+    }
+
+    return prime
+}