Each named build configuration can have defaults for any of the options that apply to the various build targets, such as `build`, `serve`, and `test`. The [Angular CLI](cli) `build`, `serve`, and `test` commands can then replace files with appropriate versions for your intended target environment.
### Using environment-specific variables in your app
The following application structure configures build targets for production and staging environments:
```
└── src
└── app
├── app.component.html
└── app.component.ts
└── environments
├── environment.prod.ts
├── environment.staging.ts
└── environment.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 default environment
}
title = 'app works!';
}
```
{@a file-replacement}
## Configure target-specific file replacements
The main CLI configuration file, `angular.json`, contains a `fileReplacements` section in the configuration for each build target, which allows you to replace any file 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": {
"production": {
"fileReplacements": [
{
"replace": "src/environments/environment.ts",
"with": "src/environments/environment.prod.ts"
}
],
...
```
This means that when you build your production configuration (using `ng build --prod` or `ng build --configuration=production`), the `src/environments/environment.ts` file is replaced with the target-specific version of the file, `src/environments/environment.prod.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": {
"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.
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`:
As applications grow in functionality, they also grow in size.
The CLI allows you to 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](#app-environments).
```
{
...
"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:
* 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 and error when a given part of the app reaches or exceeds a boundary size that you set.
Each budget entry is a JSON object with the following properties:
Internally, Autoprefixer relies on a library called [Browserslist](https://github.com/browserslist/browserslist) to figure out which browsers to support with prefixing.
Browserlist looks for configuration options in a `browserslist` property of the package configuration file, or in a configuration file named `.browserslistrc`.
Autoprefixer looks for the `browserslist` configuration when it prefixes your CSS.
If you want to produce a progressive web app and are using [Lighthouse](https://developers.google.com/web/tools/lighthouse/) to grade the project, add the following browserslist entry to your `package.json` file, in order to eliminate the [old flexbox](https://developers.google.com/web/tools/lighthouse/audits/old-flexbox) prefixes:
```
"browserslist": [
"last 2 versions",
"not ie <= 10",
"not ie_mob <= 10"
]
```
</div>
{@a proxy}
## Proxying to a backend server
You can use the [proxying support](https://webpack.js.org/configuration/dev-server/#devserver-proxy) in the `webpack` dev server to divert certain URLs to a backend server, by passing a file to the `--proxy-config` build option.
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.
```
const PROXY_CONFIG = {
"/api/proxy": {
"target": "http://localhost:3000",
"secure": false,
"bypass": function (req, res, proxyOptions) {
if (req.headers.accept.indexOf("html") !== -1) {
console.log("Skipping proxy for browser request.");
return "/index.html";
}
req.headers["X-Custom-Header"] = "yes";
}
}
}
module.exports = PROXY_CONFIG;
```
### Using corporate proxy
If you work behind a corporate proxy, the 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:
<code-examplelanguage="none"class="code-shell">
npm install --save-dev https-proxy-agent
</code-example>
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.
```
var HttpsProxyAgent = require('https-proxy-agent');
var proxyConfig = [{
context: '/api',
target: 'http://your-remote-server.com:3000',
secure: false
}];
function setupForCorporateProxy(proxyConfig) {
var proxyServer = process.env.http_proxy || process.env.HTTP_PROXY;
