What is the difference between call and apply?

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 array and C for comma."

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

3 years ago

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 array and C for comma."

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

3 years ago

To answer the part about when to use each function, use apply if you don't know the number of arguments you will be passing, or if they are already in an array or array-like object (like the arguments object to forward your own arguments. Use call otherwise, since there's no need to wrap the arguments in an array.

f.call(thisObject, a, b, c); // Fixed number of arguments



f.apply(thisObject, arguments); // Forward this function's arguments



var args = [];

while (...) {

    args.push(some_value());

}

f.apply(thisObject, args); // Unknown number of arguments

When I'm not passing any arguments (like your example), I prefer call since I'm calling the function. apply would imply you are applying the function to the (non-existent) arguments.

There shouldn't be any performance differences, except maybe if you use apply and wrap the arguments in an array (e.g. f.apply(thisObject, [a, b, c]) instead of f.call(thisObject, a, b, c)). I haven't tested it, so there could be differences, but it would be very browser specific. It's likely that call is faster if you don't already have the arguments in an array and apply is faster if you do.

3 years ago