TypeScript: augmenting built-in types

Types are ‘open ended’ in TypeScript, so you can just write:

interface Array {
  shuffle: () => any; // <-- Whatever signature you want.

And then the type is expanded to include the new function (and you can assign a function matching the signature to it).

Note however that extending the built-in types (those in lib.d.ts – such as Array) has an issue currently in the language service, as it caches those internally for perf reasons. Do the workaround I wrote-up at http://typescript.codeplex.com/workitem/4 to extend the built-in types without errors in the language service in VS.

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