Rediscovering JavaScript

Use === Instead of ==

Many JavaScript programmers, including your humble author, often repeat the mistake of comparing using ==, which is the type-coercion non-strict equality operator. Let’s look at an example that shows why using == may be a bad idea.

gotchas/double-equals.js

//BROKEN CODE
const a = '1';
const b = 1;
const c = '1.0';

console.log(a == b);
console.log(b == c);
console.log(a == c);

In the short piece of code, the constants a, b, and c have values ’1’, 1, and ’1.0’, respectively. One value is of number type and the other two are of string type. The last three lines compare each combination of the constants. Suppose a is equal to b and b is equal to c; then logically JavaScript should tell us that a is equal ...