At first glance, it might seem like you can interchange ?? (Nullish Coalescing Operator) and || (Logical OR) in JavaScript. However, they are fundamentally different in how they handle truthy and falsy values.
Falsy Values in JavaScript
Falsy values become false in a Boolean context:
**0
undefined
null
NaN
false
” (empty string)**
Truthy Values
Everything else.
The Difference Explained
|| (Logical OR): Returns the first truthy value. If the first operand is falsy, it returns the second operand.
Here, 0 is falsy, so “default” is returned.
?? (Nullish Coalescing): Returns the right-hand operand if the left-hand operand is null or undefined. It ignores other falsy values.
Here, 0 is not null or undefined, so 0 is returned.
Use Cases
Use || when you want to provide a fallback for any falsy value.
Use ?? when you only want to provide a fallback for null or undefined.
Understanding this difference helps avoid bugs and ensures your code behaves as expected.
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