== compares two values after converting them to the same type if needed ("loose equality"), while === compares both value and type without any conversion ("strict equality").
This is one of the most common sources of unexpected behavior for developers new to JavaScript, because == can produce surprising results.
0 == false // true — false converts to 0
"5" == 5 // true — "5" converts to number 5
null == undefined // true — special case0 === false // false — different types
"5" === 5 // false — different types
null === undefined // false — different typesBecause == performs implicit type conversion before comparing, it can produce results that don't match intuition. Most modern JavaScript style guides recommend always using === (and its counterpart !==) to avoid these surprises, reserving == only for the rare cases where the conversion behavior is genuinely intended.
Last reviewed: September 2026