Today I Learned - Rocky Kev

TIL of the difference between || and ??

POSTED ON:

TAGS: javascript boolean stackoverflow

What is ||? That's logical OR.

What is ??? That's nullish coalescing.

Both operators are often used to provide a default value if the first one is missing.

The main difference:

|| is checking ONLY for falsy.

?? is checking for null or undefined.

The problem with ||:

console.log(12 || "not found") // 12
console.log(0  || "not found") // "not found"

console.log(12 ?? "not found") // 12
console.log(0  ?? "not found") // 0

/////////
console.log("jane" || "not found") // "jane"
console.log(""     || "not found") // "not found"

console.log("jane" ?? "not found") // "jane"
console.log(""     ?? "not found") // ""

/////////
console.log(true  || "not found") // true
console.log(false || "not found") // "not found"

console.log(true  ?? "not found") // true
console.log(false ?? "not found") // false

You can start to see where the || can become problematic, and you're always safer to use ??.

via DMeechan's Stack Overflow comment

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