What is the use of the JavaScript 'bind' method?

Question

What is the use of bind() in JavaScript?

Answer 1

bind allows-

• set the value of "this" to an specific object. This becomes very helpful as sometimes this is not what is intended.
• reuse methods
• curry a function

For example, you have a function to deduct monthly club fees

function getMonthlyFee(fee){
  var remaining = this.total - fee;
  this.total = remaining;
  return this.name +' remaining balance:'+remaining;
}

Now you want to reuse this function for a different club member. Note that the monthly fee will vary from member to member.

Let's imagine Rachel has a balance of 500, and a monthly membership fee of 90.

var rachel = {name:'Rachel Green', total:500};

Now, create a function that can be used again and again to deduct the fee from her account every month

//bind
var getRachelFee = getMonthlyFee.bind(rachel, 90);
//deduct
getRachelFee();//Rachel Green remaining balance:410
getRachelFee();//Rachel Green remaining balance:320

Now, the same getMonthlyFee function could be used for another member with a different membership fee. For Example, Ross Geller has a 250 balance and a monthly fee of 25

var ross = {name:'Ross Geller', total:250};
//bind
var getRossFee = getMonthlyFee.bind(ross, 25);
//deduct
getRossFee(); //Ross Geller remaining balance:225
getRossFee(); //Ross Geller remaining balance:200