fix(jest): default isolatedModules to true for faster compilation (fixes #1899)#2191
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fix(jest): default isolatedModules to true for faster compilation (fixes #1899)#2191
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#1899) Angular 19 introduced signals, new control flow syntax, and standalone-by-default components. These produce significantly more complex TypeScript that causes the ts-jest language service (used when isolatedModules: false) to build a full cross-file Program per test file, resulting in severe slowdowns (reports of 2 min → 15 min test runs). Root cause: when isolatedModules is false (previously the implicit default), ts-jest instantiates a TypeScript LanguageService and rebuilds a full Program for each file. Angular 19+'s richer type surface makes this path prohibitively slow. Fix: set isolatedModules: true in the builder's default transformer options. This switches ts-jest to its fast per-file transpile path, matching the recommendation from jest-preset-angular's own example apps since v14.4.0. Cross-file type checking is better served by tsc --noEmit or ng build. Users who need the previous behaviour can opt out in their jest.config.ts: transform: { '^.+\.(ts|js|mjs|html|svg)$': ['jest-preset-angular', { isolatedModules: false }] } BREAKING CHANGE: isolatedModules now defaults to true. This disables cross-file TypeScript type checking during jest runs. Targeted for the next major version.
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just-jeb
added
breaking-change
builders:jest
enhancement
…exHtmlTransformer (fixes #1899) - Add target.configuration to factory plugin example in README (alongside existing target.project) - Update indexHtmlTransformer examples (JS and TS) to include the target param with comments - Add integration test 'target-options-in-plugin-and-transformer' that builds with a real factory plugin and indexHtmlTransformer, both using target.configuration, then verifies the value appears in the JS bundle and index.html meta tag - Add esbuild/define-configuration-plugin.js and esbuild/configuration-transformer.js to sanity-esbuild-app as the test fixtures
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Problem
Reporters upgrading from
@angular-builders/jest@18to@19see dramatic test run slowdowns (e.g. 2 min → 15 min). The root cause is not the builder version itself — it is the interaction between Angular 19 complexity and ts-jest's compilation path.How ts-jest decides which path to take:
isolatedModules: false(previous implicit default) → ts-jest creates a TypeScript LanguageService and builds a full cross-file Program for every test file → slowisolatedModules: true→ ts-jest uses a fast per-file transpile path → fastWhy Angular 19 made this worse: Angular 19 introduced signals, new control flow syntax, and standalone-by-default components. These produce significantly richer TypeScript that gives the language service much more work per file. The slowness was latent before; Angular 19 made it visible.
Why the builder is responsible: The builder constructs the
transformoptions inresolveForProject()without settingisolatedModules, so ts-jest defaults tofalse. Users have no obvious way to know they need to override this.Fix
Set
isolatedModules: truein the builder's default transformer options. This matches the recommendation in jest-preset-angular's own docs and example apps since v14.4.0.Users who need cross-file type checking during
ng testcan opt out via theirjest.config.ts:For most teams, cross-file type checking is better handled by
tsc --noEmitorng build.Breaking Change
This is a BREAKING CHANGE:
isolatedModulesnow defaults totrue, disabling cross-file TypeScript type checking during jest runs. This PR is intentionally targeting the next major version and should not be merged into the current major.Tests
DefaultConfigResolver.resolveForProject()to assertisolatedModules: truein the transform optionsFixes #1899