Why == and === behave differently in JavaScript

Source: Dev.to

Strict Equality (===)

=== checks two things:

1. Are the values the same?
2. Are the types the same?

Both conditions must be met.

5 === 5               // true
5 === "5"             // false
true === 1            // false
null === undefined    // false

If the types don’t match, JavaScript returns false without any conversion.

Loose Equality (==)

== tries to be “helpful” by converting values before comparing them (type coercion).

5 == "5"               // true  (string → number)
true == 1              // true  (boolean → number)
false == 0             // true
null == undefined      // true  (special case)

Some surprising cases

"" == 0                // true
"0" == 0               // true
[] == 0                // true

Why This Happens

When using ==, JavaScript automatically attempts to make the operands the same type:

These implicit steps are why == can produce confusing results.

Which One Should You Use?

For beginners—and in most cases—prefer strict equality:

// Use ===

It’s predictable and avoids unexpected type coercion.
Use == only when you fully understand the conversion rules or need the special case null == undefined.

Simple Demo

console.log(0 == false);   // true
console.log(0 === false);  // false

console.log("5" == 5);     // true
console.log("5" === 5);    // false

Running these snippets in the console shows the difference instantly.

Quick Summary

Short version

• === is strict and predictable.
• == performs type coercion and can be messy.

Use === for cleaner logic and fewer surprises.