What is the difference between call and apply?

What is the difference between using call and apply to invoke a function?

var func = function(){
  alert('hello!');
};

func.apply();

vs

func.call();

Are there performance differences between the two methods? When is it best to use call over apply and vice versa?




Answer

The difference is that apply lets you invoke the function with arguments as an array; call requires the parameters be listed explicitly. A useful mnemonic is A for a rray and C for c omma.”

See MDN’s documentation on apply and call .

Pseudo syntax:

theFunction.apply(valueForThis, arrayOfArgs) theFunction.call(valueForThis, arg1, arg2, …)

There is also, as of ES6, the possibility to spread the array for use with the call function, you can see the compatibilities here .

Sample code:

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"]); // used with the spread operator

// Output: 

// My name is John and I am a fireman.
// My name is Susan and I am a school teacher.
// My name is Claude and I am a mathematician.
// My name is Matthew and I am a physicist.