Extend Date prototype with a interface Typescript

Question

I want to add a getWeekNumber function to the Date prototype in javascript / typescript. I want to do it with an interface becease otherwise I get a error that he does not k

Answer 1

You can do it this way:

in DateExt.ts:

interface Date 
{
    getWeekNumber: () => number;
}

Date.prototype.getWeekNumber = function() 
{
    return 123;//your calculations goes here
};

in your app.ts:

import './DateExt';

let a = new Date();
console.log(a.getWeekNumber());