Creating a custom definition file for TypeScript

Currently, I am facing an issue with a third-party library that provides global functions similar to jQuery ($ .functionName()), but unfortunately there is no definition file available. Due to this, my attempt to write my own file has been unsuccessful as the reference/import mechanism does not seem to be functioning properly.

Surprisingly, if I include my declarations directly in the code, it works perfectly:

declare let a: string;

myClass {
   constructor() {
       console.log(a);
   }
}

However, when I try to declare it in a separate file, things don't work out as expected:

myDeclaration.d.ts

export declare let a: string;

myClass.ts

/// <reference path="myDeclaration.d.ts" />

myClass {
   constructor() {
       console.log(a);
   }
}

I even attempted to use

import * as a from "myDeclaration"
, but unfortunately it keeps throwing the error: Cannot find name 'a'

Answer №1

Avoid using export with ambient declarations.

To fix this, simply remove the export from your .d.ts file:

declare let a:string

In most cases, you can also omit the <reference path=""> as the declaration will be accessible throughout your project.

Use export declare when creating a definition for a module that is imported, such as a JS npm library, and opt for an ambient definition when the object is globally available without needing an import (like jQuery loaded via <script> tag).

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