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Building and Testing Angular

This document describes how to set up your development environment to build and test Angular. It also explains the basic mechanics of using git, node, and yarn.

See the contribution guidelines if you'd like to contribute to Angular.

Prerequisite Software

Before you can build and test Angular, you must install and configure the following products on your development machine:

Getting the Sources

Fork and clone the Angular repository:

  1. Login to your GitHub account or create one by following the instructions given here.
  2. Fork the main Angular repository.
  3. Clone your fork of the Angular repository and define an upstream remote pointing back to the Angular repository that you forked in the first place.
# Clone your GitHub repository:
git clone git@github.com:<github username>/angular.git

# Go to the Angular directory:
cd angular

# Add the main Angular repository as an upstream remote to your repository:
git remote add upstream https://github.com/angular/angular.git

Installing NPM Modules

Next, install the JavaScript modules needed to build and test Angular:

# Install Angular project dependencies (package.json)
yarn install


To build Angular run:

yarn build

Running Tests Locally

Bazel is used as the primary tool for building and testing Angular.

To see how to run and debug Angular tests locally please refer to the Bazel Testing Angular section.

Note that you should execute all test suites before submitting a PR to GitHub (yarn test //packages/...).

However, affected tests will be executed on our CI infrastructure. So if you forgot to run some affected tests which would fail, GitHub will indicate the error state and present you the failures.

PRs can only be merged if the code is formatted properly and all tests are passing.

Testing changes against a local library/project

Often for developers the best way to ensure the changes they have made work as expected is to run use changes in another library or project. To do this developers can build Angular locally, and using yarn link build a local project with the created artifacts.

This can be done by running:

yarn ng-dev misc build-and-link <path-to-local-project-root>

Building and serving a project


When making changes to Angular packages and testing in a local library/project you need to run ng cache disable to disable the Angular CLI disk cache. If you are making changes that are not reflected in your locally served library/project, verify if you have CLI Cache disabled.

Invoking the Angular CLI

The Angular CLI needs to be invoked using Node.js --preserve-symlinks flag. Otherwise the symbolic links will be resolved using their real path which causes node module resolution to fail.

node --preserve-symlinks --preserve-symlinks-main node_modules/@angular/cli/lib/init.js serve

Formatting your source code

Angular uses clang-format to format the source code. If the source code is not properly formatted, the CI will fail and the PR cannot be merged.

You can automatically format your code by running:

A better way is to set up your IDE to format the changed file on each file save.

VS Code

  1. Install Clang-Format extension for VS Code.
  2. It will automatically pick up the settings from .vscode/settings.json. If you haven't already, create a settings.json file by following the instructions here.

WebStorm / IntelliJ

  1. Install the ClangFormatIJ plugin
  2. Open Preferences->Tools->clang-format
  3. Find the field named "PATH"
  4. Add <PATH_TO_YOUR_WORKSPACE>/angular/node_modules/clang-format/bin/<OS>/ where the OS options are: darwin_x64, linux_x64, and win32.


  1. Install Vim Clang-Format.
  2. Create a project-specific .vimrc in your Angular directory containing
let g:clang_format#command = '$ANGULAR_PATH/node_modules/.bin/clang-format'

where $ANGULAR_PATH is an environment variable of the absolute path of your Angular directory.

Linting/verifying your Source Code

You can check that your code is properly formatted and adheres to coding style by running:

$ yarn lint

Publishing Snapshot Builds

When a build of any branch on the upstream fork angular/angular is green on CircleCI, it automatically publishes build artifacts to repositories in the Angular org. For example, the @angular/core package is published to https://github.com/angular/core-builds.

You may find that your un-merged change needs some validation from external participants. Rather than requiring them to pull your Pull Request and build Angular locally, they can depend on snapshots of the Angular packages created based on the code in the Pull Request.

Getting Packages from Build Artifacts

Each CI run for a Pull Request stores the built Angular packages as build artifacts. The artifacts are not guaranteed to be available as a long-term distribution mechanism, but they are guaranteed to be available around the time of the build.

You can access the artifacts for a specific CI run by going to the workflow page, clicking on the publish_packages_as_artifacts job and then switching to the "ARTIFACTS" tab.

Archives for each Package

On the "Artifacts" tab, there is a list of links to compressed archives for Angular packages. The archive names are of the format <package-name>-pr<pr-number>-<sha>.tgz (for example core-pr12345-a1b2c3d.tgz).

One can use the URL to the .tgz file for each package to install them as dependencies in a project they need to test the Pull Request changes against. Both npm and yarn support installing dependencies from URLs to .tgz files, for example by updating the dependencies in package.json to point to the artifact URLs and then running npm/yarn install:

"dependencies": {
  "@angular/common": "https://<...>.circle-artifacts.com/0/angular/common-pr12345-a1b2c3d.tgz",
  "@angular/core": "https://<...>.circle-artifacts.com/0/angular/core-pr12345-a1b2c3d.tgz",
  "...": "..."

Download all Packages

In addition to the individual package archives, a .tgz file including all packages is also available (named all-pr<pr-number>-<sha>.tgz). This can be used if one prefers to download all packages locally and test them by either of the following ways:

  1. Update the dependencies in package.json to point to the local uncompressed package directories.

  2. Directly copy the local uncompressed package directories into the node_modules/ directory of a project.

Note that (while faster) the second approach has limitations. For example: a. Any transitive dependencies of the copied packages will not be automatically updated. b. The packages need to be copied over every time npm/yarn install is run. c. Some package managers (such as pnpm or yarn pnp) might not work correctly.

Publishing to GitHub Repos

You can also manually publish *-builds snapshots just like our CircleCI build does for upstream builds. Before being able to publish the packages, you need to build them locally by running the yarn build command.

First time, you need to create the GitHub repositories:

$ export TOKEN=[get one from https://github.com/settings/tokens]
$ CREATE_REPOS=1 ./scripts/ci/publish-build-artifacts.sh [GitHub username]

For subsequent snapshots, just run:

$ ./scripts/ci/publish-build-artifacts.sh [GitHub username]

The script will publish the build snapshot to a branch with the same name as your current branch, and create it if it doesn't exist.

Bazel Support


VS Code

  1. Install Bazel extension for VS Code.

WebStorm / IntelliJ

  1. Install the Bazel plugin
  2. You can find the settings under Preferences->Other Settings->Bazel Settings

It will automatically recognize *.bazel and *.bzl files.

Remote Build Execution and Remote Caching

Bazel builds in the Angular repository use a shared cache. When a build occurs a hash of the inputs is computed and checked against available outputs in the shared cache. If an output is found, it is used as the output for the build action rather than performing the build locally.

Remote Build Execution requires authentication as a google.com account.

--config=remote flag

The --config=remote flag can be added to enable remote execution of builds.