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:

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

Here is an example

  1. // 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 {};