description: Hugo Pipes can process JavaScript files with [ESBuild](https://github.com/evanw/esbuild).
date: 2020-07-20
publishdate: 2020-07-20
lastmod: 2020-07-20
categories: [asset management]
keywords: []
menu:
docs:
parent: "pipes"
weight: 45
weight: 45
sections_weight: 45
draft: false
---
Any JavaScript resource file can be transpiled and "tree shaken" using `js.Build` which takes for argument either a string for the filepath or a dict of options listed below.
### Options
targetPath [string]
: If not set, the source path will be used as the base target path.
Note that the target path's extension may change if the target MIME type is different, e.g. when the source is TypeScript.
Note that this is meant for small data sets, e.g. config settings. For larger data, please put/mount the files into `/assets` and import them directly.
: There is/was a bug in WebKit with severe performance issue with the tracking of TDZ checks in JavaScriptCore. Enabling this flag removes the TDZ and `const` assignment checks and may improve performance of larger JS codebases until the WebKit fix is in widespread use. See https://bugs.webkit.org/show_bug.cgi?id=199866
> Marking a package as external doesn't imply that the library can be loaded from a CDN. It simply tells Hugo not to expand/include the package in the JS file.
Default is `iife`, a self-executing function, suitable for inclusion as a <script> tag.
sourceMap
: Whether to generate source maps. Enum, currently only `inline` (we will improve that).
### Import JS code from /assets
{{<new-in"0.78.0">}}
Since Hugo `v0.78.0``js.Build` has full support for the virtual union file system in [Hugo Modules](/hugo-modules/). You can see some simple examples in this [test project](https://github.com/gohugoio/hugoTestProjectJSModImports), but in short this means that you can do this:
```js
import { hello } from 'my/module';
```
And it will resolve to the top-most `index.{js,ts,tsx,jsx}` inside `assets/my/module` in the layered file system.
```js
import { hello3 } from 'my/module/hello3';
```
Wil resolve to `hello3.{js,ts,tsx,jsx}` inside `assets/my/module`.
Any imports starting with `.` is resolved relative to the current file:
```js
import { hello4 } from './lib';
```
For other files (e.g. `JSON`, `CSS`) you need to use the relative path including any extension, e.g:
```js
import * as data from 'my/module/data.json';
```
Any imports in a file outside `/assets` or that does not resolve to a component inside `/assets` will be resolved by [ESBuild](https://esbuild.github.io/) with the **project directory** as the resolve directory (used as the starting point when looking for `node_modules` etc.). Also see [hugo mod npm pack](/commands/hugo_mod_npm_pack/). If you have any imported NPM dependencies in your project, you need to make sure to run `npm install` before you run `hugo`.
Also note the new `params` option that can be passed from template to your JS files, e.g.:
Hugo will, by default, generate a `assets/jsconfig.json` file that maps the imports. This is useful for navigation/intellisense help inside code editors, but if you don't need/want it, you can [turn it off](/getting-started/configuration/#configure-build).
### Include Dependencies In package.json / node_modules
Any imports in a file outside `/assets` or that does not resolve to a component inside `/assets` will be resolved by [ESBuild](https://esbuild.github.io/) with the **project directory** as the resolve directory (used as the starting point when looking for `node_modules` etc.). Also see [hugo mod npm pack](/commands/hugo_mod_npm_pack/). If you have any imported NPM dependencies in your project, you need to make sure to run `npm install` before you run `hugo`.
{{<new-in"0.78.1">}} From Hugo `0.78.1` the start directory for resolving NPM packages (aka. packages that live inside a `node_modules` folder) is always the main project folder.
**Note:** If you're developing a theme/component that is supposed to be imported and depends on dependencies inside `package.json`, we recommend reading about [hugo mod npm pack](/commands/hugo_mod_npm_pack/), a tool to consolidate all the NPM dependencies in a project.
It's a common practice to load external libraries using a content delivery network (CDN) rather than importing all packages in a single JS file. To load scripts from a CDN with Hugo, you'll need to shim the libraries as follows. In this example, `react` and `react-dom` will be shimmed.
First, add React and ReactDOM [CDN script tags](https://reactjs.org/docs/add-react-to-a-website.html#tip-minify-javascript-for-production) in your HTML template files. Then create `assets/js/shims/react.js` and `assets/js/shims/react-dom.js` with the following contents:
```js
// In assets/js/shims/react.js
module.exports = window.React;
// In assets/js/shims/react-dom.js
module.exports = window.ReactDOM;
```
Finally, add the following to your project's `package.json`:
This tells Hugo's `js.Build` command to look for `react` and `react-dom` in the project's `assets/js/shims` folder. Note that the `browser` field in your `package.json` file will cause React and ReactDOM to be excluded from your JavaScript bundle. Therefore, **it is unnecessary to add them to the `js.Build` command's `externals` argument.**
