JavaScript Building

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.
params [map or slice]: Params that can be imported as JSON in your JS files, e.g.:

{{ $js := resources.Get "js/main.js" | js.Build (dict "params" (dict "api" "https://example.org/api")) }}

And then in your JS file:

import * as params from '@params';

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.

minify [bool]: Let js.Build handle the minification.
avoidTDZ: 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
target [string]: The language target. One of: es5, es2015, es2016, es2017, es2018, es2019, es2020 or esnext. Default is esnext.
externals [slice]: External dependencies. If a dependency should not be included in the bundle (Ex. library loaded from a CDN.), it should be listed here.

{{ $externals := slice "react" "react-dom" }}

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.

defines [map]: Allow to define a set of string replacement to be performed when building. Should be a map where each key is to be replaced by its value.

{{ $defines := dict "process.env.NODE_ENV" `"development"` }}

format [string]: The output format. One of: iife, cjs, esm. Default is iife, a self-executing function, suitable for inclusion as a tag.
sourceMap: Whether to generate source maps. Enum, currently only inline (we will improve that).

Import JS code from /assets

Since Hugo v0.78.0 js.Build has full support for the virtual union file system in Hugo Modules. You can see some simple examples in this test project, but in short this means that you can do this:

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.

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:

import { hello4 } from './lib';

For other files (e.g. JSON, CSS) you need to use the relative path including any extension, e.g:

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 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. 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.:

{{ $js := resources.Get "js/main.js" | js.Build (dict "params" (dict "api" "https://example.org/api")) }}

And then in your JS file:

import * as params from '@params';

Hugo will, by default, generate a assets/jsconfig.js 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.

Include Dependencies In package.json / node_modules

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, a tool to consolidate all the NPM dependencies in a project.

Examples

{{ $built := resources.Get "js/index.js" | js.Build "main.js" }}

Or with options:

{{ $externals := slice "react" "react-dom" }}
{{ $defines := dict "process.env.NODE_ENV" `"development"` }}

{{ $opts := dict "targetPath" "main.js" "externals" $externals "defines" $defines }}
{{ $built := resources.Get "scripts/main.js" | js.Build $opts }}
<script type="text/javascript" src="{{ $built.RelPermalink }}" defer></script>

Shimming a JS library

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 in your HTML template files. Then create assets/js/shims/react.js and assets/js/shims/react-dom.js with the following contents:

// 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:

{
  "browser": {
    "react": "./assets/js/shims/react.js",
    "react-dom": "./assets/js/shims/react-dom.js"
  }
}

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.

That’s it! You should now have a browser-friendly JS which can use external JS libraries.