resolve-typescript-plugin

A webpack plugin to resolve TypeScript files imported using the .js extension when using ESM imports.

Obsolete

webpack has equivalent functionality built-in since v5.74.0. This plugin is no longer needed unless you are using an older version of webpack.

To migrate from this plugin, set resolve.extensionAlias in webpack.config.js:

export default {
    resolve: {
        extensionAlias: {
            ".js": [".ts", ".js"],
            ".mjs": [".mts", ".mjs"]
        }
    }
};

and remove new ResolveTypeScriptPlugin() from resolve.plugins.

For the time being this plugin is still maintained for the benefit of people who use older versions of webpack.

Why?

If you are using webpack in conjunction with TypeScript and ES Modules, you need this plugin for full compliance with the ES Modules ecosystem.

ES Modules require imports to specify the runtime path of the file to be imported, including file extension. For TypeScript files, this means that you must import using the extension .js even though the source file uses the extension .ts or .tsx. This is because TypeScript compiles to a .js file that will be used at runtime.

However, webpack behaves differently, even when configured for ES Modules. webpack expects that files will be imported by specifying the compile-time path of the file, including the compile-time extension. For TypeScript files this will be .ts or .tsx. Alternatively, webpack expects that files will be imported with no extension, in which case webpack will resolve the extension automatically according to the resolve.extensions option. Neither of these behaviours is consistent with browser or node ES Module environments.

This plugin extends webpack module resolution so that imports specifying a .js extension will resolve to the corresponding .ts or .tsx file if available, and fall back to .js otherwise.

If you want to create ES Modules in TypeScript that are consistent between webpack, browser, and node environments, use this plugin.

See ts-loader#1110 for more background on this issue.

Install

With npm:

npm install --save-dev resolve-typescript-plugin

or yarn:

yarn add --dev resolve-typescript-plugin

Usage

Include the following in package.json to configure your project to be an ES Module:

{
    "type": "module"
}

Include something like the following in webpack.config.js:

import ResolveTypeScriptPlugin from "resolve-typescript-plugin";

export default {
    module: {
        rules: [
            {
                test: /\.tsx?$/,
                use: "ts-loader"
            }
        ]
    },
    resolve: {
        plugins: [new ResolveTypeScriptPlugin()]
    }
};

You will also need to have ts-loader (or another TypeScript loader) installed and configured.

Previous versions of this README recommended setting resolve.fullySpecified to true. This is no longer recommended because it breaks compatibility with webpack-dev-server and possibly other webpack tooling.

If you use this plugin, you should probably remove .ts and .tsx from resolve.extensions.

Options

Pass options to the plugin as an argument to the constructor, as follows:

new ResolveTypeScriptPlugin({
    includeNodeModules: false
});

includeNodeModules

By default, the plugin does not resolve TypeScript files inside node_modules subdirectories. To enable this, set includeNodeModules: true.

Default: false.

Webpack 4 Compatibility

This plugin supports webpack versions 4.x and 5.x. However, there are some caveats when using webpack 4.x in conjunction with ES modules.

Webpack 4.x does not support webpack.config files in ES module format, so if you set "type": "module" in package.json then you must mark the webpack.config file as a CommonJS file by naming it webpack.config.cjs (with a .cjs extension). Of course, you must also use CommonJS format, for example:

const ResolveTypeScriptPlugin = require("resolve-typescript-plugin");

module.exports = {
    module: {
        rules: [
            {
                test: /\.tsx?$/,
                use: "ts-loader"
            }
        ]
    },
    resolve: {
        plugins: [new ResolveTypeScriptPlugin()]
    }
};

Webpack 4.x also will not discover the webpack.config file automatically if it is named with a .cjs extension, so you must specify the path to the configuration file explicitly when running webpack, for example: webpack --config ./webpack.config.cjs.

Webpack 5.x has none of these caveats. In Webpack 5.x, configuration files may be in ES Module or CommonJS format, and will be discovered automatically if they are named with any of .js, .cjs, or .mjs file extensions.

Feedback

Please report bugs, problems, and missing features on the GitHub Issue Tracker.