Nanananananananana.. Pat Man!
Learn about our RFC process, Open RFC meetings & more.Join in the discussion! »


2.0.1 • Public • Published


TypeScript custom transformer that strips assertions in production code. It is intended to be used with ts-simple-assert but other assert libraries may work too.

In other words, it takes this:

import { assert } from "ts-simple-assert";
assert(something === someOtherThingThatShouldBeEqualToSomething);
return assert(false);   // Sometimes useful for making the TypeScript compiler happy
                        // by marking some code that should be unreachable

and turns it into this:

    void 0;
    return void 0;

Yep. They're gone. OK, actually it doesn't remove the comments but you get the picture. void 0 simply means undefined and it can be removed by your a JavaScript minifier.

Version 1 of ts-transformer-unassert used to completely remove call statements and return statements only. The current version removes all expressions and replaces them with void 0. Both versions completely remove import statements.

Getting Started


ts-transformer-unassert requires an up-to-date version of typescript and a task runner capable of running TypeScript custom transformers. It's been only tested with webpack and ts-loader.


npm install --save-dev ts-transformer-unassert

Using with webpack and ts-loader

Add this at the top of your production webpack.config.js:

const unassert = require("ts-transformer-unassert").default;

And add the following option to your ts-loader options:

getCustomTransformers: () => ({ before: [unassert] })

The ts-loader readme points to some more info on how to run custom transformers.

Building and Running the tests

Building and running the (extremely simplistic) tests requires a Unix-like shell environment. Clone the repo, install the dependencies, build, and finally run the tests with the following commands:

git clone
cd ts-transformer-unassert
npm install
npm run build
npm test

The tests consists of creating a bundle with webpack without using ts-transformer-unassert; running it to make sure that it fails (because of an assert(false); line in the code); recreating the same bundle, this time using ts-transformer-unassert; and running it to make sure that it doesn't fail anymore (because the assert call has been stripped).


  • Fatih Aygün - Initial work - cyco130


npm i ts-transformer-unassert

DownloadsWeekly Downloads






Last publish


  • avatar