Call vs. Apply in JavaScript: When Should I Use Which?

Call vs. Apply: Unveiling the Differences in Function Invocation

In JavaScript, invoking a function can be accomplished through various methods, with Function.prototype.apply() and Function.prototype.call() being two prominent choices. However, these methods exhibit key differences that can influence their suitability in different scenarios.

Functional Similarity

Both call and apply share a common purpose: they facilitate the invocation of a function. However, the manner in which they handle arguments differs significantly.

apply (ValueForThis, ArrayOfArgs)

The apply() method requires two arguments: the value to be bound to the "this" keyword within the function, and an array containing the arguments that the function should receive. The apply() method expands the array into individual arguments before passing them to the function.

call (ValueForThis, Arg1, Arg2, ...)

In contrast, the call() method allows the arguments to be passed as distinct parameters, similar to how regular function calls are made. The value bound to the "this" keyword is specified as the first argument, followed by the remaining arguments that the function requires.

Performance Considerations

Benchmarking reveals that call is marginally faster than apply in most scenarios. This is because call operates with a slightly lower overhead, since it does not require the additional processing involved in expanding the arguments.

Practical Considerations

The distinction between call and apply lies primarily in their suitability for handling different types of arguments.

• Use call when passing a fixed number of arguments explicitly.
• Consider apply when invoking a function with a variable number of arguments or when you need to pass an array as an argument.

Example Usage

The provided code snippet demonstrates the usage of both call and apply:

function theFunction(name, profession) {
    console.log("My name is " + name + " and I am a " + profession +".");
}
theFunction("John", "fireman");
theFunction.apply(undefined, ["Susan", "school teacher"]);
theFunction.call(undefined, "Claude", "mathematician");
theFunction.call(undefined, ...["Matthew", "physicist"]); // using the spread operator

Understanding the nuances of call and apply empowers developers to invoke functions effectively, tailoring their approach based on the nature of the arguments and performance considerations.

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