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 know the method getWeekNumber().

First I tried with a standart Date interface like this:

interface Date {
    getWeekNumber(): number;
}

This had the resolve that all the methods of the Date are not call able anymore.

I want to know of there is a way to extend the Date with an interface.

score 9 · Accepted Answer · answered Mar 30 '16 at 09:09

9

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());

answered Mar 30 '16 at 09:09

Amid

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The problem with that solution is that all the Date methods are not avaible anymore like `getTime()` or `getDate()` – Martijn Bakker Mar 30 '16 at 09:31
They are available. Its an issue with your IDE. I have latest VSCode / Typescript and it works like a charm. – Amid Mar 30 '16 at 09:46
also my ionic CLI crasht and the application itself – Martijn Bakker Mar 30 '16 at 10:13
Sorry my fault. I exported the interface and imported it with {Date} – Martijn Bakker Apr 01 '16 at 08:09

Extend Date prototype with a interface Typescript

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