80 lines
2.8 KiB
Markdown
80 lines
2.8 KiB
Markdown
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# Migration to `ngcc` npm `postinstall` script
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## What does this schematic do?
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This schematic adds an [Angular compatibility compiler](guide/ngcc), or `ngcc`, invocation to npm/yarn's `postinstall` script in the `package.json` of an Angular CLI workspace.
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This script is invoked after each execution of `npm install` and modifies `node_modules` by converting any found Angular libraries to a format that is compatible with Angular version 9.
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An example diff might look like the following:
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**Before:**
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```json
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"scripts": {
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"ng": "ng",
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"start": "ng serve",
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"build": "ng build",
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"test": "ng test",
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"lint": "ng lint",
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"e2e": "ng e2e"
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},
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```
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**After:**
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```json
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"scripts": {
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"ng": "ng",
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"start": "ng serve",
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"build": "ng build",
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"test": "ng test",
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"lint": "ng lint",
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"e2e": "ng e2e",
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"postinstall": "ngcc --properties es2015 browser module main --first-only --create-ivy-entry-points"
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},
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```
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If the `package.json` already contains a `postinstall` script, then the `ngcc` invocation will be prepended to the current command:
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**Before:**
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```json
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"scripts": {
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...
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"postinstall": "some-command"
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},
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```
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**After:**
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```json
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"scripts": {
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...
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"postinstall": "ngcc --properties es2015 browser module main --first-only --create-ivy-entry-points && some-command"
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},
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```
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## Why is this migration necessary?
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This migration is a build performance optimization that enables `ngcc` to parallelize the compilation of npm libraries.
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An application build performed via CLI's `ng build` should succeed regardless of this `postinstall` script being installed, because the CLI has `ngcc` built-in.
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However, this built-in `ngcc` can't parallelize the compilation of multiple libraries, and therefore often takes considerably longer to run.
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## Can I customize the `ngcc` options in the `postinstall` script?
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By default the `postinstall` script invokes `ngcc` with options to compile only the most commonly needed library formats.
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For some projects, especially those that depend on the CommonJS distribution of Angular (for example, Angular Universal apps), it might be beneficial to modify the `postinstall` script to also compile the CommonJS distribution of the library:
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```json
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"scripts": {
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...
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"postinstall": "ngcc --properties es2015 browser module main --first-only --create-ivy-entry-points && ngcc --properties main --create-ivy-entry-points"
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},
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```
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For the full set of options run `npx ngcc --help` or `yarn ngcc --help`.
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## Will libraries compiled with `ngcc` still be compatible with Angular version 8?
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Yes, the migration causes `ngcc` to be invoked with the `--create-ivy-entry-points` flag, which ensures that the `ngcc` compilation is non-destructive, so the same `node_modules` can be used with Angular version 8 and version 9.
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