jpcasa
12/21/2018 - 4:23 PM

JS: Bind, Call, Apply

Use .bind() when you want that function to later be called with a certain context, useful in events. Use .call() or .apply() when you want to invoke the function immediately, with modification of the context.

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Function calls: call, apply and bind

All of these three methods are used to attach this into function and the difference is in the function invocation.

.call() invokes the function immediately and requires you to pass in arguments as a list (one by one).

.apply() invokes the function immediately and allows you to pass in arguments as an array.

.call() and .apply() are mostly equivalent and are used to borrow a method from an object. Choosing which one to use depends on which one is easier to pass the arguments in. Just decide whether it’s easier to pass in an array or a comma separated list of arguments.

Quick tip: Apply for Array — Call for Comma.

const Snow = {surename: 'Snow'}

const char = {
  surename: 'Stark',
  knows: function(arg, name) {
    console.log(`You know ${arg}, ${name} ${this.surename}`);
  }
}

char.knows('something', 'Bran');              // You know something, Bran Stark
char.knows.call(Snow, 'nothing', 'Jon');      // You know nothing, Jon Snow
char.knows.apply(Snow, ['nothing', 'Jon']);   // You know nothing, Jon Snow