Equality: == vs ===

JavaScript has two ways to check equality, and they behave very differently.

Double Equals == - With Type Coercion

The == operator performs type coercion before comparing:

Copyconsole.log(1 == "1") // true (converts string "1" to number 1)

console.log(0 == false) // true (0 is "falsy")
console.log("" == false) // true (empty string is "falsy")

Why? JavaScript converts these values to the same type before comparing. Zero and empty strings are considered "falsy" values that equal false.

Triple Equals === - No Type Coercion

The === operator compares both value and type without any coercion:

Copyconsole.log(1 === 1) // true (same type and value)
console.log(1 === "1") // false (different types)
console.log(0 === false) // false (different types)
console.log("" === false) // false (different types)

Not Equals: != vs !==

The same rules apply to not equals:

Copyconsole.log(1 != "1") // false (converts types, then compares)
console.log(1 !== "1") // true (different types, so not equal)

Which To Use?

Always prefer === and !== to avoid unexpected type coercion issues.

The Exception: null and undefined

There's one case where == is actually useful - checking for null or undefined:

Copyconsole.log(null == null) // true
console.log(null == undefined) // true (null and undefined are considered equal)

console.log(null === null) // true
console.log(null === undefined) // false (different types)

When checking if a variable has a value, you often want to catch both null and undefined which is why == is useful here.