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Global: Modifying Module

Global-modifying Modules

A global-modifying module alters existing values in the global scope when they are imported. For example, there might exist a library which adds new members to String.prototype when imported. This pattern is somewhat dangerous due to the possibility of runtime conflicts, but we can still write a declaration file for it.

Identifying global-modifying modules

Global-modifying modules are generally easy to identify from their documentation. In general, they’re similar to global plugins, but need a require call to activate their effects.

You might see documentation like this:

// 'require' call that doesn't use its return value
var unused = require("magic-string-time");
/* or */
var x = "hello, world";
// Creates new methods on built-in types
var y = [1, 2, 3];
// Creates new methods on built-in types

Here is an example

// Type definitions for [~THE LIBRARY NAME~] [~OPTIONAL VERSION NUMBER~]
// Project: [~THE PROJECT NAME~]
// Definitions by: [~YOUR NAME~] <[~A URL FOR YOU~]>
/*~ This is the global-modifying module template file. You should rename it to index.d.ts
*~ and place it in a folder with the same name as the module.
*~ For example, if you were writing a file for "super-greeter", this
*~ file should be 'super-greeter/index.d.ts'
/*~ Note: If your global-modifying module is callable or constructable, you'll
*~ need to combine the patterns here with those in the module-class or module-function
*~ template files
declare global {
/*~ Here, declare things that go in the global namespace, or augment
*~ existing declarations in the global namespace
interface String {
fancyFormat(opts: StringFormatOptions): string;
/*~ If your module exports types or values, write them as usual */
export interface StringFormatOptions {
fancinessLevel: number;
/*~ For example, declaring a method on the module (in addition to its global side effects) */
export function doSomething(): void;
/*~ If your module exports nothing, you'll need this line. Otherwise, delete it */
export {};

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Last updated: Apr 19, 2021