For example, when you want to work with JavaScript code which extends another library.
\n\ntsimport { greeter } from \"super-greeter\";\n\n// Normal Greeter API\ngreeter(2);\ngreeter(\"Hello world\");\n\n// Now we extend the object with a new function at runtime\nimport \"hyper-super-greeter\";\ngreeter.hyperGreet();
The definition for “super-greeter”:
\n\nts/*~ This example shows how to have multiple overloads for your function */\nexport interface GreeterFunction {\n (name: string): void\n (time: number): void\n}\n\n/*~ This example shows how to export a function specified by an interface */\nexport const greeter: GreeterFunction;
We can extend the existing module like the following:
\n\nts// Type definitions for [~THE LIBRARY NAME~] [~OPTIONAL VERSION NUMBER~]\n// Project: [~THE PROJECT NAME~]\n// Definitions by: [~YOUR NAME~] <[~A URL FOR YOU~]>\n\n/*~ This is the module plugin template file. You should rename it to index.d.ts\n *~ and place it in a folder with the same name as the module.\n *~ For example, if you were writing a file for \"super-greeter\", this\n *~ file should be 'super-greeter/index.d.ts'\n */\n\n/*~ On this line, import the module which this module adds to */\nimport { greeter } from \"super-greeter\";\n\n/*~ Here, declare the same module as the one you imported above\n *~ then we expand the existing declaration of the greeter function\n */\nexport module \"super-greeter\" {\n export interface GreeterFunction {\n /** Greets even better! */\n hyperGreet(): void;\n }\n}
This uses declaration merging
\nSome plugins add or modify top-level exports on existing modules.\nWhile this is legal in CommonJS and other loaders, ES6 modules are considered immutable and this pattern will not be possible.\nBecause TypeScript is loader-agnostic, there is no compile-time enforcement of this policy, but developers intending to transition to an ES6 module loader should be aware of this.
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