Javascript: call(), apply() and bind()

In simple words,

• Call invokes the function and allows you to pass in arguments one by one.

• Apply invokes the function and allows you to pass in arguments as an array.

• Bind returns a new function, allowing you to pass in a this array and any number of arguments.

Call and apply are some what interchangeable. We can decide on basis of whether it’s easier to send in an array or a comma separated list of arguments to a function.

A bind function is basically which binds the context of something and then stores it into a variable for execution at a later stage. A Bind is different than Call and Apply as it returns a new function. Whereas Call and Apply execute the current function immediately. Bind doesn't execute function immediately, but returns wrapped apply function.

Call Example:

var person1 = {firstName: 'Harry', lastName: 'Potter'};
var person2 = {firstName: 'Kane', lastName: 'Smith'};

function say(greeting) {
    console.log(greeting + ' ' + this.firstName + ' ' + this.lastName);
}

say.call(person1, 'Hello'); // Hello Harry Potter
say.call(person2, 'Hello'); // Hello Kane Smith

Apply Example:

 var person1 = {firstName: 'Harry', lastName: 'Potter'};
 var person2 = {firstName: 'Kane', lastName: 'Smith'};

 function say(greeting) {
    console.log(greeting + ' ' + this.firstName + ' ' + this.lastName);
 } 
say.apply(person1, ['Hello']); // Hello Harry Potter
say.apply(person2, ['Hello']); // Hello Kane Smith

Bind Example:

 var person1 = {firstName: 'Harry', lastName: 'Potter'};
 var person2 = {firstName: 'Kane', lastName: 'Smith'};

function say() {
    console.log('Hello ' + this.firstName + ' ' + this.lastName);
}

var sayHelloHarry = say.bind(person1);
var sayHelloKane = say.bind(person2);

sayHelloHarry();   // Hello Harry Potter
sayHelloKane();    // Hello Kane Smith

The basic difference between Call, Apply and Bind ==> Bind will be used if you want your execution context to come later in the picture.

Trick to remember, Call is for comma separated list and Apply is for Array.