Building and serving Angular apps

This page discusses build-specific configuration options for Angular projects.

Configuring application environments

You can define different named build configurations for your project, such as development and staging, with different defaults.

Each named configuration can have defaults for any of the options that apply to the various builder targets, such as build, serve, and test. The Angular CLI build, serve, and test commands can then replace files with appropriate versions for your intended target environment.

Configure environment-specific defaults

Using the Angular CLI, start by running the generate environments command shown here to create the src/environments/ directory and configure the project to use these files.

ng generate environments

The project's src/environments/ directory contains the base configuration file, environment.ts, which provides configuration for production, the default environment. You can override default values for additional environments, such as development and staging, in target-specific configuration files.

For example:

myProject/src/environments
  environment.ts
  environment.development.ts
  environment.staging.ts

The base file environment.ts, contains the default environment settings. For example:

export const environment = {
  production: true
};

The build command uses this as the build target when no environment is specified. You can add further variables, either as additional properties on the environment object, or as separate objects. For example, the following adds a default for a variable to the default environment:

export const environment = {
  production: true,
  apiUrl: 'http://my-prod-url'
};

You can add target-specific configuration files, such as environment.development.ts. The following content sets default values for the development build target:

export const environment = {
  production: false,
  apiUrl: 'http://my-api-url'
};

Using environment-specific variables in your app

The following application structure configures build targets for development and staging environments:

src
  app
    app.component.html
    app.component.ts
  environments
    environment.ts
    environment.development.ts
    environment.staging.ts

To use the environment configurations you have defined, your components must import the original environments file:

import { environment } from './../environments/environment';

This ensures that the build and serve commands can find the configurations for specific build targets.

The following code in the component file (app.component.ts) uses an environment variable defined in the configuration files.

import { Component } from '@angular/core';
  import { environment } from './../environments/environment';

  @Component({
    selector: 'app-root',
    templateUrl: './app.component.html',
    styleUrls: ['./app.component.css']
  })
  export class AppComponent {
    constructor() {
      console.log(environment.production); // Logs false for development environment
    }

    title = 'app works!';
  }

Configure target-specific file replacements

The main CLI configuration file, angular.json, contains a fileReplacements section in the configuration for each build target, which lets you replace any file in the TypeScript program with a target-specific version of that file. This is useful for including target-specific code or variables in a build that targets a specific environment, such as production or staging.

By default no files are replaced. You can add file replacements for specific build targets. For example:

"configurations": {
    "development": {
      "fileReplacements": [
          {
            "replace": "src/environments/environment.ts",
            "with": "src/environments/environment.development.ts"
          }
        ],
        …

This means that when you build your development configuration with ng build --configuration development, the src/environments/environment.ts file is replaced with the target-specific version of the file, src/environments/environment.development.ts.

You can add additional configurations as required. To add a staging environment, create a copy of src/environments/environment.ts called src/environments/environment.staging.ts, then add a staging configuration to angular.json:

"configurations": {
    "development": { … },
    "production": { … },
    "staging": {
      "fileReplacements": [
        {
          "replace": "src/environments/environment.ts",
          "with": "src/environments/environment.staging.ts"
        }
      ]
    }
  }

You can add more configuration options to this target environment as well. Any option that your build supports can be overridden in a build target configuration.

To build using the staging configuration, run the following command:

ng build --configuration=staging

You can also configure the serve command to use the targeted build configuration if you add it to the "serve:configurations" section of angular.json:

"serve": {
    "builder": "@angular-devkit/build-angular:dev-server",
    "options": {
      "browserTarget": "your-project-name:build"
    },
    "configurations": {
      "development": {
        "browserTarget": "your-project-name:build:development"
      },
      "production": {
        "browserTarget": "your-project-name:build:production"
      },
      "staging": {
        "browserTarget": "your-project-name:build:staging"
      }
    }
  },

Configuring size budgets

As applications grow in functionality, they also grow in size. The CLI lets you set size thresholds in your configuration to ensure that parts of your application stay within size boundaries that you define.

Define your size boundaries in the CLI configuration file, angular.json, in a budgets section for each configured environment.

{
  …
  "configurations": {
    "production": {
      …
      "budgets": []
    }
  }
}

You can specify size budgets for the entire app, and for particular parts. Each budget entry configures a budget of a given type. Specify size values in the following formats:

Size value	Details
123 or 123b	Size in bytes.
123kb	Size in kilobytes.
123mb	Size in megabytes.
12%	Percentage of size relative to baseline. (Not valid for baseline values.)

When you configure a budget, the build system warns or reports an error when a given part of the application reaches or exceeds a boundary size that you set.

Each budget entry is a JSON object with the following properties:

Property	Value
type	The type of budget. One of: Value Details bundle The size of a specific bundle. initial The size of JavaScript needed for bootstrapping the application. Defaults to warning at 500kb and erroring at 1mb. allScript The size of all scripts. all The size of the entire application. anyComponentStyle This size of any one component stylesheet. Defaults to warning at 2kb and erroring at 4kb. anyScript The size of any one script. any The size of any file.
name	The name of the bundle (for type=bundle).
baseline	The baseline size for comparison.
maximumWarning	The maximum threshold for warning relative to the baseline.
maximumError	The maximum threshold for error relative to the baseline.
minimumWarning	The minimum threshold for warning relative to the baseline.
minimumError	The minimum threshold for error relative to the baseline.
warning	The threshold for warning relative to the baseline (min & max).
error	The threshold for error relative to the baseline (min & max).

Configuring CommonJS dependencies

It is recommended that you avoid depending on CommonJS modules in your Angular applications. Depending on CommonJS modules can prevent bundlers and minifiers from optimizing your application, which results in larger bundle sizes. Instead, it is recommended that you use ECMAScript modules in your entire application. For more information, see How CommonJS is making your bundles larger.

The Angular CLI outputs warnings if it detects that your browser application depends on CommonJS modules. To disable these warnings, add the CommonJS module name to allowedCommonJsDependencies option in the build options located in angular.json file.

"build": {
  "builder": "@angular-devkit/build-angular:browser",
  "options": {
     "allowedCommonJsDependencies": [
        "lodash"
     ]
     …
   }
   …
},

Configuring browser compatibility

The Angular CLI uses Browserslist to ensure compatibility with different browser versions. Autoprefixer is used for CSS vendor prefixing and @babel/preset-env for JavaScript syntax transformations.

Internally, the Angular CLI uses the below browserslist configuration which matches the browsers that are supported by Angular.

last 2 Chrome versions
  last 1 Firefox version
  last 2 Edge major versions
  last 2 Safari major versions
  last 2 iOS major versions
  Firefox ESR

To override the internal configuration, run ng generate config browserslist, which generates a .browserslistrc configuration file in the the project directory.

See the browserslist repository for more examples of how to target specific browsers and versions.

Use browsersl.ist to display compatible browsers for a browserslist query.

Proxying to a backend server

Use the proxying support in the webpack development server to divert certain URLs to a backend server, by passing a file to the --proxy-config build option. For example, to divert all calls for http://localhost:4200/api to a server running on http://localhost:3000/api, take the following steps.

1. Create a file proxy.conf.json in your project's src/ folder.

2. Add the following content to the new proxy file:

   {
     "/api": {
       "target": "http://localhost:3000",
       "secure": false
     }
   }

3. In the CLI configuration file, angular.json, add the proxyConfig option to the serve target:

   …
     "architect": {
       "serve": {
         "builder": "@angular-devkit/build-angular:dev-server",
         "options": {
           "browserTarget": "your-application-name:build",
           "proxyConfig": "src/proxy.conf.json"
         },
   …

4. To run the development server with this proxy configuration, call ng serve.

Edit the proxy configuration file to add configuration options; following are some examples. For a description of all options, see webpack DevServer documentation.

NOTE: If you edit the proxy configuration file, you must relaunch the ng serve process to make your changes effective.

Rewrite the URL path

The pathRewrite proxy configuration option lets you rewrite the URL path at run time. For example, specify the following pathRewrite value to the proxy configuration to remove "api" from the end of a path.

{
  "/api": {
    "target": "http://localhost:3000",
    "secure": false,
    "pathRewrite": {
      "^/api": ""
    }
  }
}

If you need to access a backend that is not on localhost, set the changeOrigin option as well. For example:

{
  "/api": {
    "target": "http://npmjs.org",
    "secure": false,
    "pathRewrite": {
      "^/api": ""
    },
    "changeOrigin": true
  }
}

To help determine whether your proxy is working as intended, set the logLevel option. For example:

{
  "/api": {
    "target": "http://localhost:3000",
    "secure": false,
    "pathRewrite": {
      "^/api": ""
    },
    "logLevel": "debug"
  }
}

Proxy log levels are info (the default), debug, warn, error, and silent.

Proxy multiple entries

You can proxy multiple entries to the same target by defining the configuration in JavaScript.

Set the proxy configuration file to proxy.conf.mjs (instead of proxy.conf.json), and specify configuration files as in the following example.

export default [
  {
    context: [
        '/my',
        '/many',
        '/endpoints',
        '/i',
        '/need',
        '/to',
        '/proxy'
    ],
    target: 'http://localhost:3000',
    secure: false
  }
];

In the CLI configuration file, angular.json, point to the JavaScript proxy configuration file:

…
"architect": {
  "serve": {
    "builder": "@angular-devkit/build-angular:dev-server",
    "options": {
      "browserTarget": "your-application-name:build",
      "proxyConfig": "src/proxy.conf.mjs"
    },
…

Bypass the proxy

If you need to optionally bypass the proxy, or dynamically change the request before it's sent, add the bypass option, as shown in this JavaScript example.

export default {
  '/api/proxy': {
    "target": 'http://localhost:3000',
    "secure": false,
    "bypass": function (req, res, proxyOptions) {
        if (req.headers.accept.includes('html')) {
            console.log('Skipping proxy for browser request.');
            return '/index.html';
        }
        req.headers['X-Custom-Header'] = 'yes';
    }
  }
};

Using corporate proxy

If you work behind a corporate proxy, the backend cannot directly proxy calls to any URL outside your local network. In this case, you can configure the backend proxy to redirect calls through your corporate proxy using an agent:

npm install --save-dev https-proxy-agent

When you define an environment variable http_proxy or HTTP_PROXY, an agent is automatically added to pass calls through your corporate proxy when running npm start.

Use the following content in the JavaScript configuration file.

import HttpsProxyAgent from 'https-proxy-agent';

const proxyConfig = [{
  context: '/api',
  target: 'http://your-remote-server.com:3000',
  secure: false
}];

export default (proxyConfig) => {
  const proxyServer = process.env.http_proxy || process.env.HTTP_PROXY;
  if (proxyServer) {
    const agent = new HttpsProxyAgent(proxyServer);
    console.log('Using corporate proxy server: ' + proxyServer);

    for (const entry of proxyConfig) {
      entry.agent = agent;
    }
  }

  return proxyConfig;
};