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A collection of utilities to take your TypeScript development up a notch

(you can cherrypick what you import)


Three GIFs to convince you that you need tsafe in your life

Assert things you know are true, get runtime errors where you were wrong:

Implement compile time unit testing


Make TypeScript believe whatever you say:


Powerful TypeScript features like assertion functions or user-defined type guards are only useful if paired with utility functions.

TypeScript, however, only exports type helpers (e.g. Record, ReturnType, etc.).

This module provides «the missing builtins» such as the assert function and corrects frustrating aspects of default utility types such as ReturnType.

Documentation website


tsafe is both an NPM and a Deno module. (Achieved with denoify)

Import in deno:

import { assert, typeGuard, ... } from "";

Install elsewhere:

$ npm install --save tsafe
$ yarn add tsafe