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Automatically discover and add missing types in your TypeScript code
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Automatically discover and add missing types in your TypeScript code.


Build Status Coverage Status code style: prettier


TypeWiz monitors your variable types in runtime, and uses this information to add missing type annotations to your TypeScript code. For instance, given the following source code as input:

function add(a, b) {
    return a + b;
add(5, 6);

TypeWiz will automatically detect the types of a and b as number, and will rewrite to code to read:

function add(a: number, b: number) {
    return a + b;
add(5, 6);

You can learn more about the project in the blog posts:


For front-end code, please have a look at the TypeWiz WebPack Plugin.

For node.js code, please check out the typewiz-node Runner.

To use TypeWiz from the command line try the TypeWiz CLI.

If you are interested in creating your own custom integration, see the Integration Test for an example how to directly use the TypeWiz API. You can use the API directly by adding this library to your project:

yarn add -D typewiz-core


npm install --save-dev typewiz-core

Configuration options

Configuration options can be specified using the typewiz.json configuration file. This file is used by typewiz-node and typewiz-webpack and can be parsed using the ConfigurationParser class in typewiz-core for custom integrations.

The typewiz.json file has the following format:

        "prefix":"TypeWiz |"


  • rootDir: string (default: undefined) - If given, all the file paths in the collected type info will be resolved relative to this directory.

  • tsConfig: string (default: undefined) - The path to your project's tsconfig.json file. This is required for several other options, like instrumenting implicit this and type inference using static analysis.

  • instrumentCallExpressions: boolean (default: false) - Try to find even more types by combining static analysis with the runtime analysis. TypeWiz will try to use TypeScript's inferred types when determining the type of a function argument. See #27 for an example.

  • instrumentImplicitThis: boolean (default: false) - Find type of this in non-class member functions. See #33 for discussion.

  • skipTwizDeclarations: boolean (default: false) - Don't add a declaration of $_$twiz to instrumented files.

  • prefix: string (default: '') - A prefix to add before each type added by applyTypes(). See #11.


Copyright (C) 2018, Uri Shaked. Licensed under the MIT license.

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