Custom ESBuild builders for Angular build facade

Allow customizing ESBuild configuration

Table of Contents

• Usage
  • For Example
• Builders
  • Custom ESBuild application
    • Example
  • Custom ESBuild dev-server
    • Example
  • Custom ESBuild unit-test
    • Example
• Index Transform
  • Example
• ES Modules (ESM) Support

This documentation is for the latest major version only

⚠️ Version alignment: The major version of @angular-builders/custom-esbuild must match the major version of @angular/core in your project. For example, Angular 19 requires @angular-builders/custom-esbuild@19.x, Angular 20 requires @angular-builders/custom-esbuild@20.x, etc. Using a mismatched version is the most common source of issues.

Previous versions

• Version 21
• Version 20
• Version 19
• Version 18
• Version 17

Prerequisites:

• Angular CLI 22

Usage

1. npm i -D @angular-builders/custom-esbuild
2. In your angular.json:

   "projects": {
     ...
     "[project]": {
       ...
       "architect": {
         ...
         "[architect-target]": {
           "builder": "@angular-builders/custom-esbuild:[application|dev-server|unit-test]",
           "options": {
             ...
           }

   Where:
   • [project] is the name of the project to which you want to add the builder
   • [architect-target] is the name of build target you want to run (build, serve, test etc. or any custom target)
   • [application|dev-server|unit-test] one of the supported builders - application, dev-server, or unit-test
3. If [architect-target] is not one of the predefined targets (like build, serve, test etc.) then run it like this:
   ng run [project]:[architect-target]
   If it is one of the predefined targets, you can run it with ng [architect-target]

For Example

• angular.json:

  "projects": {
    ...
    "example-app": {
      ...
      "architect": {
        ...
        "build": {
          "builder": "@angular-builders/custom-esbuild:browser",
          "options": {
            ...
          }

• Run the build: ng build

Builders

• @angular-builders/custom-esbuild:application
• @angular-builders/custom-esbuild:dev-server
• @angular-builders/custom-esbuild:unit-test

Custom ESBuild application

The @angular-builders/custom-esbuild:application builder is an extension of the @angular-devkit/build-angular:application builder, allowing the specification of additional properties on top of the existing ones. The custom builder runs the original builder at the end, incorporating extra parameters specified in the extended configuration. It will also perform index.html transformations if specified.

Builder options:

• All the @angular-devkit/build-angular:application options
• plugins
• indexHtmlTransformer: see below

Example

angular.json:

"architect": {
  ...
  "build": {
    "builder": "@angular-builders/custom-esbuild:application",
    "options": {
      "plugins": ["./esbuild/plugins.ts", { "path": "./esbuild/define-env.ts", "options": { "stage": "development" } }],
      "indexHtmlTransformer": "./esbuild/index-html-transformer.js",
      "outputPath": "dist/my-cool-client",
      "index": "src/index.html",
      "browser": "src/main.ts",
      "polyfills": ["zone.js"],
      "tsConfig": "src/tsconfig.app.json"
    },
    "configurations": {
      "production": {
        "plugins": ["./esbuild/plugins.ts", { "path": "./esbuild/define-env.ts", "options": { "stage": "production" } }]
      }
    }
  }

In the above example, we specify the list of plugins that should implement the ESBuild plugin schema. These plugins are custom user plugins and are added to the original ESBuild Angular configuration. Additionally, the indexHtmlTransformer property is used to specify the path to the file that exports the function used to modify the index.html.

The plugin file can export either a single plugin, a list of plugins or a factory function that returns a plugin or list of plugins. If a plugin accepts configuration then the config should be provided in angular.json:

// esbuild/plugins.ts
import type { Plugin, PluginBuild } from 'esbuild';

const defineTextPlugin: Plugin = {
  name: 'define-text',
  setup(build: PluginBuild) {
    const options = build.initialOptions;
    options.define.buildText = JSON.stringify('This text is provided during the compilation');
  },
};

export default defineTextPlugin;

OR:

// esbuild/plugins.ts
import type { Plugin, PluginBuild } from 'esbuild';

function defineEnv(pluginOptions: { stage: string }): Plugin {
  return {
    name: 'define-env',
    setup(build: PluginBuild) {
      const buildOptions = build.initialOptions;
      buildOptions.define.stage = JSON.stringify(pluginOptions.stage);
    },
  };
}

export default defineEnv;

Or:

// esbuild/plugins.ts
import type { Plugin, PluginBuild } from 'esbuild';

const defineTextPlugin: Plugin = {
  name: 'define-text',
  setup(build: PluginBuild) {
    const options = build.initialOptions;
    options.define.buildText = JSON.stringify('This text is provided during the compilation');
  },
};

const updateExternalPlugin: Plugin = {
  name: 'update-external',
  setup(build: PluginBuild) {
    const options = build.initialOptions;
    options.external ??= [];
    options.external.push('elysia');
  },
};

export default [defineTextPlugin, updateExternalPlugin];

Or:

// esbuild/plugins.ts
import type { Plugin, PluginBuild } from 'esbuild';
import type { ApplicationBuilderOptions } from '@angular-devkit/build-angular';
import type { Target } from '@angular-devkit/architect';

export default (builderOptions: ApplicationBuilderOptions, target: Target): Plugin => {
  return {
    name: 'define-text',
    setup(build: PluginBuild) {
      const options = build.initialOptions;
      // target.project is the Angular project name (e.g. "my-app")
      options.define.currentProject = JSON.stringify(target.project);
      // target.configuration is the active build configuration (e.g. "production", "staging")
      options.define.currentConfiguration = JSON.stringify(target.configuration ?? 'default');
    },
  };
};

Custom ESBuild dev-server

The @angular-builders/custom-esbuild:dev-server is an enhanced version of the @angular-devkit/build-angular:dev-server builder that allows the specification of middlewares (Vite's Connect functions). It also obtains plugins and indexHtmlTransformer from the :application configuration to run the Vite server with all the necessary configuration applied.

Example

angular.json:

"architect": {
  ...
  "build": {
    "builder": "@angular-builders/custom-esbuild:application",
    "options": {
      "plugins": ["./esbuild/plugin-1.js"]
      ...
    }
  },
  "serve": {
    "builder": "@angular-builders/custom-esbuild:dev-server",
    "options": {
      "middlewares": ["./esbuild/my-middleware.js"],
      "buildTarget": "my-project:build"
    }
  }

Custom ESBuild unit-test

The @angular-builders/custom-esbuild:unit-test builder is an enhanced version of the @angular/build:unit-test builder that reuses your application ESBuild plugins during test execution. It reads the plugins from the referenced :application build target and runs the official unit test builder with those plugins applied. There is no need to specify a runner option as the only supported test runner is Vitest.

Example-1

angular.json:

"architect": {
  ...
  "build": {
    "builder": "@angular-builders/custom-esbuild:application",
    "options": {
      "plugins": ["./esbuild/plugin-1.js"]
      ...
    }
  },
  "test": {
    "builder": "@angular-builders/custom-esbuild:unit-test",
    "options": {
      "buildTarget": "my-project:build",
      "tsConfig": "src/tsconfig.spec.json"
    }
  }
}

Index Transform

Since Angular 8, index.html is not generated as part of the build. If you want to modify your index.html, you should use the indexHtmlTransformer option. indexHtmlTransformer is a path (relative to the workspace root) to a .js or .ts file that exports a transformation function for index.html. If indexHtmlTransformer is written in TypeScript, the application's tsConfig file will be used by tsnode for its execution:

(indexHtmlContent: string, target: Target) => string | Promise<string>;

or, in other words, the function receives target options and original index.html content (generated by Angular CLI) and returns a new content as string or Promise<string>.

The indexHtmlTransformer function signature is defined here.

It is useful when you want to transform your index.html according to the build options.

Example

angular.json:

"architect": {
  ...
  "build": {
    "builder": "@angular-builders/custom-esbuild:application",
    "options": {
      "indexHtmlTransformer": "./esbuild/index-html-transformer.js"
      ...
    }

index-html-transformer.js:

module.exports = (indexHtml, target) => {
  // target.configuration is the active build configuration (e.g. "production", "staging")
  // target.project is the Angular project name
  const i = indexHtml.indexOf('</body>');
  const content = `<p>Dynamically inserted content</p>`;
  return `${indexHtml.slice(0, i)}
            ${content}
            ${indexHtml.slice(i)}`;
};

Alternatively, using TypeScript:

import type { Target } from '@angular-devkit/architect';

export default (indexHtml: string, target: Target) => {
  // target.configuration is the active build configuration (e.g. "production", "staging")
  // target.project is the Angular project name
  const i = indexHtml.indexOf('</body>');
  const content = `<p>Dynamically inserted content</p>`;
  return `${indexHtml.slice(0, i)}
            ${content}
            ${indexHtml.slice(i)}`;
};

In the example we add a paragraph with an example content to your index.html. It is a very simple example without any asynchronous code but you can also return a Promise from this function.

ES Modules (ESM) Support

Custom ESBuild builder fully supports ESM.

• If your app has "type": "module" both plugin.js and index-html-transformer.js will be treated as ES modules, unless you change their file extension to .cjs. In that case they'll be treated as CommonJS Modules. Example.
• For "type": "commonjs" (or unspecified type) both plugin.js and index-html-transformer.js will be treated as CommonJS modules unless you change their file extension to .mjs. In that case they'll be treated as ES Modules. Example.
• TypeScript plugins and transformers work in both CommonJS and ESM projects with no extra setup — just point the builder at your .ts file. (Earlier versions required forcing a ts-node/esm loader through NODE_OPTIONS; that is no longer necessary.) TypeScript path aliases are supported in both module formats.

Type-checking TypeScript plugins and transformers

.ts plugins and indexHtmlTransformer files are loaded with jiti and transpiled, not type-checked, at build time. Your editor still type-checks them as you write. To enforce type-checking in CI, add a dedicated tsconfig that includes them and run tsc:

tsconfig.build-config.json:

{
  "extends": "./tsconfig.json",
  "compilerOptions": { "noEmit": true },
  "include": ["plugins/**/*.ts", "index-html-transformer.ts"],
}

tsc --noEmit -p tsconfig.build-config.json