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| 1 | +# Migration to `ngcc` npm `postinstall` script |
| 2 | + |
| 3 | +## What does this schematic do? |
| 4 | + |
| 5 | +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. |
| 6 | +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. |
| 7 | + |
| 8 | +An example diff might look like the following: |
| 9 | + |
| 10 | +**Before:** |
| 11 | + |
| 12 | +```json |
| 13 | + "scripts": { |
| 14 | + "ng": "ng", |
| 15 | + "start": "ng serve", |
| 16 | + "build": "ng build", |
| 17 | + "test": "ng test", |
| 18 | + "lint": "ng lint", |
| 19 | + "e2e": "ng e2e" |
| 20 | + }, |
| 21 | +``` |
| 22 | + |
| 23 | +**After:** |
| 24 | + |
| 25 | +```json |
| 26 | + "scripts": { |
| 27 | + "ng": "ng", |
| 28 | + "start": "ng serve", |
| 29 | + "build": "ng build", |
| 30 | + "test": "ng test", |
| 31 | + "lint": "ng lint", |
| 32 | + "e2e": "ng e2e", |
| 33 | + "postinstall": "ngcc --properties es2015 browser module main --first-only --create-ivy-entry-points" |
| 34 | + }, |
| 35 | +``` |
| 36 | + |
| 37 | +If the `package.json` already contains a `postinstall` script, then the `ngcc` invocation will be prepended to the current command: |
| 38 | + |
| 39 | +**Before:** |
| 40 | +```json |
| 41 | + "scripts": { |
| 42 | + ... |
| 43 | + "postinstall": "some-command" |
| 44 | + }, |
| 45 | +``` |
| 46 | + |
| 47 | +**After:** |
| 48 | +```json |
| 49 | + "scripts": { |
| 50 | + ... |
| 51 | + "postinstall": "ngcc --properties es2015 browser module main --first-only --create-ivy-entry-points && some-command" |
| 52 | + }, |
| 53 | +``` |
| 54 | + |
| 55 | + |
| 56 | +## Why is this migration necessary? |
| 57 | + |
| 58 | +This migration is a build performance optimization that enables `ngcc` to parallelize the compilation of npm libraries. |
| 59 | +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. |
| 60 | +However, this built-in `ngcc` can't parallelize the compilation of multiple libraries, and therefore often takes considerably longer to run. |
| 61 | + |
| 62 | + |
| 63 | +## Can I customize the `ngcc` options in the `postinstall` script? |
| 64 | + |
| 65 | +By default the `postinstall` script invokes `ngcc` with options to compile only the most commonly needed library formats. |
| 66 | +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: |
| 67 | + |
| 68 | +```json |
| 69 | + "scripts": { |
| 70 | + ... |
| 71 | + "postinstall": "ngcc --properties es2015 browser module main --first-only --create-ivy-entry-points && ngcc --properties main --create-ivy-entry-points" |
| 72 | + }, |
| 73 | +``` |
| 74 | + |
| 75 | +For the full set of options run `npx ngcc --help` or `yarn ngcc --help`. |
| 76 | + |
| 77 | +## Will libraries compiled with `ngcc` still be compatible with Angular version 8? |
| 78 | + |
| 79 | +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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