How do I create a Javascript method for any variable? [duplicate]

Question

I'm not sure the question title is right. Let's say I have:

var myArray=[12, 1, 25];

I want to write a function such as the following "multiply" function so that I can:

var newArray = myArray.multiply(7)

and the result would be:

newArray=[12*7, 1*7, 25*7]

But I'm not referring only to an array. Initial variable could be a string to do something with.

Chaining is where calling a function returns a function. You're asking about adding a method to arrays. — Quentin
– Quentin, Commented Oct 12, 2017 at 9:16
I know I could do it by writing a function like function multiply(arr){process each element of arr and return result } but that's not how I want it. — CristianC
– CristianC, Commented Oct 12, 2017 at 9:19

Anurag Singh Bisht · Accepted Answer · 2017-10-12 09:21:36Z

2

You can achieve this by adding a multiply function to the prototype of Array.

See the code below.

var myArray=[12, 1, 25];

Array.prototype.multiply = function(arg) {
  return this.map(item => item*arg);
}

var newArr = myArray.multiply(7);

console.log(newArr);

answered Oct 12, 2017 at 9:21

Anurag Singh Bisht

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1 Comment

CristianC Over a year ago

This a great answer. It is what I was looking for. Array.prototype and String.prototype.

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