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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.

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.

• javascript
• date
• interface
• typescript

Share Improve this question Follow edited Mar 30, 2016 at 9:10 Amid 22.4k66 gold badges6262 silver badges5858 bronze badges asked Mar 30, 2016 at 8:53 Martijn BakkerMartijn Bakker 39511 gold badge55 silver badges1717 bronze badges

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1 Answer 1

Sorted by: Reset to default 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());

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