What is the difference between call, apply and bind?

All three let you choose the value of this for a function. call and apply run the function now. bind returns a new function for later.

• call(thisArg, a, b) runs the function immediately. You list the arguments one by one.
• apply(thisArg, [a, b]) also runs it immediately. You pass the arguments as an array, or an array-like object. To remember: apply takes an array.
• bind(thisArg, a) does not run the function. It returns a new function with this fixed forever. You can also pre-fill some first arguments. This is called partial application.

Once a function is bound, call or bind cannot change its this again. Only new still can.

Typical uses:

• bind to pass a method as a callback or event handler.
• call to borrow a method, like Array.prototype.slice.call(arguments).

Today, spread syntax fn(...args) replaces most uses of apply.