TOPIC OVERVIEW

javascript/Call Apply Bind

Three ways to control exactly what this means inside a function.

10 QuestionsAdvancedMedium Priority ~10 min read

call, apply, and bind all exist to let you explicitly set what this refers to inside a function, overriding whatever the normal call-site rules would produce. call and apply do this immediately — call takes arguments individually (fn.call(obj, a, b)), while apply takes them as an array (fn.apply(obj, [a, b])) — and both invoke the function right away with the given this.

bind is different: instead of calling the function, it returns a new function permanently bound to the given this, which is useful when you need to pass a method somewhere else (like an event handler) and guarantee it keeps its original context no matter how it's later called. That returned function's this can't be overridden again, even by another call or apply — once bound, it's locked.

What you'll walk away knowing

The difference between call and apply in how they accept arguments

Why bind returns a new function instead of invoking immediately, and when that matters

Why a bound function's this can't be reassigned later, even by call or apply

Common real-world uses: borrowing array methods for array-like objects, and preserving context in callbacks

1Describe call, apply, bind functions?ExpertHigh 2What happens if null is passed to call apply bind as this object?ExpertHigh 3Show usage of call, apply bind.ExpertHigh 4Show usage of bind.ExpertHigh

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