References

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The JavaScript Strict Inequality !== operator

Operator JavaScript All modern browsers Updated
Quick answer

The strict inequality operator !== returns true when two values are not strictly equal — different type or different value, with no coercion. 1 !== "1" is true. It's the negation of === and the not-equal check you should use by default.

Overview

!== is the strict, no-surprises "not equal." It's the negation of strict equality (===): it returns true unless the two values have the same type and the same value. Because it never coerces, 1 !== "1" is true (a number is not a string), which is exactly what you'd expect.

This is the not-equal operator to reach for by default, the partner to ===. Together they give predictable comparisons with none of the type-juggling that makes == and != error-prone.

The usual comparison caveats apply: objects compare by reference, so two look-alike objects are !== even with identical contents; and anything compared to NaN is unequal, so NaN !== NaN is true (use Number.isNaN() to test for NaN).

Syntax

a !== b

1 !== "1"     // true  (different types)
5 !== 5       // false
{} !== {}     // true  (different references)
NaN !== NaN   // true

Example

Live example 
<pre id="out" style="font:14px ui-monospace,monospace"></pre>
<script>
  const role = 'admin';

  if (role !== 'admin') {
    document.getElementById('out').textContent = 'access denied';
  } else {
    document.getElementById('out').textContent = 'welcome, admin';
  }
</script>

Best practices

  • Use !== as your default not-equal check — it avoids coercion.
  • Pair it with ===; avoid != and ==.
  • Remember objects compare by reference, so compare their fields to check contents.
  • Test for NaN with Number.isNaN(), not !==.

Frequently asked questions

What does !== do in JavaScript?
It returns true when two values are not strictly equal — different type or value — without any type coercion.
What is the difference between != and !== ?
!= coerces types first; !== does not. Use !==.
Why is 1 !== "1" true?
Because the types differ (number vs string) and !== doesn't coerce, so they're considered not equal.
Why are two identical objects !== ?
Objects compare by reference, not contents. Two separate objects are different references, so !== is true.
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