JavaScript `apply()` vs. `call()`: When Should I Use Which?

Invocation Methods in JavaScript: Exploring apply() vs. call()

When invoking functions in JavaScript, you have two primary methods at your disposal: apply() and call(). Both allow you to execute functions with a specified this value, but they differ in the way arguments are passed.

apply(thisValue, argumentsArray)

• Constructs an array from the provided argumentsArray.
• Invokes the function with the specified thisValue and the elements of the array as individual arguments.
• Example:

const func = function() {
    console.log("Hello world!");
};
func.apply(null, ["John", 35]); // Invokes "Hello world!" and logs "John" and 35.

call(thisValue, arg1, arg2, ...argN)

• Treats the arguments as individual parameters.
• Invokes the function with the specified thisValue and the arguments provided as separate values.
• Example:

func.call(null, "John", 35); // Invokes "Hello world!" and logs "John" and 35.

Mnemonics:

• Apply: A for array of arguments.
• Call: C for comma-separated arguments.

Performance Differences:

• There are generally negligible performance differences between apply() and call().
• However, apply() may be slightly faster when dealing with a large number of arguments.

Best Use Cases:

• Use apply(): When you have an array of arguments that you want to pass to a function, especially when the number of arguments is unknown in advance.
• Use call(): When you want to pass individual arguments to a function and have more control over their ordering.

ES6 Additions:

• In ES6, you can use the spread operator with call() to spread an array into individual arguments.
• Example:

func.call(null, ...["John", 35]); // Same as func.apply(null, ["John", 35]).

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