JS-033
!= vs !== explained in a JavaScript learning illustration — Checking inequality
Beginner4 min~4 min read#inequality#not-equal#strict-inequality

!= vs !==

Checking inequality

Goal

Understand the difference between != and !== in JavaScript.

Explanation

  • != checks whether values are different after possible type conversion.
  • !== checks whether values or types differ without automatic conversion.
  • Because of type conversion, != can give unexpected results.
  • For example, 0 != false returns false because JavaScript treats them as equal after conversion.
  • In most cases, it is safer to use !==.

Analogy

!= is a soft check: it may adjust values first. !== is a strict check: if types differ, the values are already considered different.

Code

console.log(0 != false);
console.log(0 !== false);

Result: false true

Common mistake

Beginners often expect 0 != false to be true. But because of type conversion, JavaScript treats them as equal.

Remember

  • ✦ != may convert types.
  • ✦ !== does not convert types.
  • ✦ In most cases, use !==.

Quick Quiz

Which operator checks inequality without type conversion?

Resources