CODEWITHSUNDEEP
typescript
Joon
Joon

Reputation: 9884

How to extend (add new prototype property) existing (already declared) classes in typescript?

I want to add new method catchAndLog to existing Promise class.

In plain JS, it's easy as Object.defineProperty(Promise.prototype, 'catchAndLog', ...). However, it seems typescript does not understand this.

How do I let typescript compiler know that Promise now has an additional member property so that it doesn't complain when I do Promise.reject('error').catchAndLog()?

Upvotes: 1

Views: 124

Answers (1)

Titian Cernicova-Dragomir
Titian Cernicova-Dragomir

Reputation: 249586

You can do it in the same way as in Javascript, the only catch is you need to add a definition for the newly added methods so that typescript knows about it.

declare global { // Remove this enclosing global if you are not in a module
    interface Promise<T> {
        catchAndLog(): Promise<T>
    }
}

Object.defineProperty(Promise.prototype, 'catchAndLog', {

})

Promise.reject('error').catchAndLog()

Upvotes: 2

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