fix(watch): trigger immediate callback for empty sources (fix #14898) by puneetdixit200 · Pull Request #14914 · vuejs/core

puneetdixit200 · 2026-06-04T03:59:48Z

Summary

Fixes #14898.

trigger the watcher callback on the explicit immediate first run before change detection can skip an empty multi-source array
add regression coverage for watch([], cb, { immediate: true })

Testing

Red before fix: pnpm test --run packages/runtime-core/__tests__/apiWatch.spec.ts -t "watching empty multiple sources with immediate: true" failed with expected "vi.fn()" to be called 1 times, but got 0 times
pnpm test --run packages/runtime-core/__tests__/apiWatch.spec.ts -t "watching empty multiple sources with immediate: true"
pnpm test --run packages/runtime-core/__tests__/apiWatch.spec.ts
pnpm test --run packages/runtime-core/__tests__/apiWatch.spec.ts packages/reactivity/__tests__/watch.spec.ts
pnpm exec prettier --check packages/reactivity/src/watch.ts packages/runtime-core/__tests__/apiWatch.spec.ts
pnpm exec eslint packages/reactivity/src/watch.ts packages/runtime-core/__tests__/apiWatch.spec.ts --max-warnings=0
git diff --check
pnpm check

AI-assisted, reviewed locally.

Summary by CodeRabbit

Bug Fixes
- Fixed watcher initialization with the immediate option so callbacks run exactly once on setup (including when watching arrays), ensuring consistent and reliable initial callback behavior.

coderabbitai · 2026-06-04T04:00:00Z

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: c194203c-83cc-403f-95bf-bcc87434335c

📥 Commits

Reviewing files that changed from the base of the PR and between a7b2f62 and a6f8783.

📒 Files selected for processing (1)

packages/runtime-core/__tests__/apiWatch.spec.ts

🚧 Files skipped from review as they are similar to previous changes (1)

packages/runtime-core/tests/apiWatch.spec.ts

📝 Walkthrough

Walkthrough

Adds immediateFirstRun to the watch() callback trigger condition so watch([], cb, { immediate: true }) invokes the callback on initialization; includes a test asserting the callback is called once with empty arrays for both new and old values.

Changes

Immediate callback execution for empty array watch

Layer / File(s)	Summary
Immediate trigger condition and test `packages/reactivity/src/watch.ts`, `packages/runtime-core/__tests__/apiWatch.spec.ts`	The `watch` job's callback condition now includes `immediateFirstRun` to force immediate invocation; a synchronous test verifies `watch([], spy, { immediate: true })` calls the callback once with `[]` for new and old values.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~8 minutes

Possibly related PRs

vuejs/core#12296: Both PRs modify the watch() internal job logic in packages/reactivity/src/watch.ts to change callback triggering/value handling.

Suggested labels

scope: reactivity, :hammer: p3-minor-bug

Suggested reviewers

edison1105

Poem

🐰 I watched the watchers wait in line,
Empty arrays, no first sign.
I hopped in quick — immediate-first-run,
Now callbacks wake with morning sun.
Tests applaud — one call, all fine.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately describes the fix for triggering immediate callbacks on empty sources and references the related issue `#14898`.
Linked Issues check	✅ Passed	The changes address the core requirement from `#14898`: ensuring watch with empty sources and immediate: true invokes the callback once, with test coverage added.
Out of Scope Changes check	✅ Passed	All changes are directly related to fixing the immediate callback trigger for empty sources, with modifications limited to watch.ts logic and corresponding test coverage.

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pkg-pr-new · 2026-06-04T06:09:41Z

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@vue/compiler-core

pnpm add https://pkg.pr.new/@vue/compiler-core@14914

npm i https://pkg.pr.new/@vue/compiler-core@14914

yarn add https://pkg.pr.new/@vue/compiler-core@14914.tgz

@vue/compiler-dom

pnpm add https://pkg.pr.new/@vue/compiler-dom@14914

npm i https://pkg.pr.new/@vue/compiler-dom@14914

yarn add https://pkg.pr.new/@vue/compiler-dom@14914.tgz

@vue/compiler-sfc

pnpm add https://pkg.pr.new/@vue/compiler-sfc@14914

npm i https://pkg.pr.new/@vue/compiler-sfc@14914

yarn add https://pkg.pr.new/@vue/compiler-sfc@14914.tgz

@vue/compiler-ssr

pnpm add https://pkg.pr.new/@vue/compiler-ssr@14914

npm i https://pkg.pr.new/@vue/compiler-ssr@14914

yarn add https://pkg.pr.new/@vue/compiler-ssr@14914.tgz

@vue/reactivity

pnpm add https://pkg.pr.new/@vue/reactivity@14914

npm i https://pkg.pr.new/@vue/reactivity@14914

yarn add https://pkg.pr.new/@vue/reactivity@14914.tgz

@vue/runtime-core

pnpm add https://pkg.pr.new/@vue/runtime-core@14914

npm i https://pkg.pr.new/@vue/runtime-core@14914

yarn add https://pkg.pr.new/@vue/runtime-core@14914.tgz

@vue/runtime-dom

pnpm add https://pkg.pr.new/@vue/runtime-dom@14914

npm i https://pkg.pr.new/@vue/runtime-dom@14914

yarn add https://pkg.pr.new/@vue/runtime-dom@14914.tgz

@vue/server-renderer

pnpm add https://pkg.pr.new/@vue/server-renderer@14914

npm i https://pkg.pr.new/@vue/server-renderer@14914

yarn add https://pkg.pr.new/@vue/server-renderer@14914.tgz

@vue/shared

pnpm add https://pkg.pr.new/@vue/shared@14914

npm i https://pkg.pr.new/@vue/shared@14914

yarn add https://pkg.pr.new/@vue/shared@14914.tgz

vue

pnpm add https://pkg.pr.new/vue@14914

npm i https://pkg.pr.new/vue@14914

yarn add https://pkg.pr.new/vue@14914.tgz

@vue/compat

pnpm add https://pkg.pr.new/@vue/compat@14914

npm i https://pkg.pr.new/@vue/compat@14914

yarn add https://pkg.pr.new/@vue/compat@14914.tgz

commit: a6f8783

github-actions · 2026-06-04T06:09:50Z

Size Report

Bundles

File	Size	Gzip	Brotli
runtime-dom.global.prod.js	106 kB (+3 B)	40.1 kB (+5 B)	36 kB (-18 B)
vue.global.prod.js	164 kB (+3 B)	60.1 kB (+10 B)	53.4 kB (-64 B)

Usages

Name	Size	Gzip	Brotli
createApp (CAPI only)	48.8 kB	19 kB	17.4 kB
createApp	56.9 kB (+3 B)	22 kB (+9 B)	20.1 kB (+11 B)
createSSRApp	61.2 kB (+3 B)	23.8 kB (+10 B)	21.7 kB
defineCustomElement	63.1 kB (+3 B)	23.9 kB (+9 B)	21.8 kB (+20 B)
overall	71.7 kB (+3 B)	27.4 kB (+5 B)	25 kB (+87 B)

edison1105 · 2026-06-04T06:34:40Z

/ecosystem-ci run

vue-bot · 2026-06-04T06:53:39Z

📝 Ran ecosystem CI: Open

suite	result	latest scheduled
vant	✅ success	✅ success
vue-i18n	✅ success	✅ success
pinia	✅ success	✅ success
primevue	✅ success	✅ success
vue-macros	✅ success	✅ success
test-utils	✅ success	✅ success
vite-plugin-vue	✅ success	✅ success
vitepress	✅ success	✅ success
vue-simple-compiler	✅ success	✅ success
quasar	✅ success	✅ success
radix-vue	❌ failure	❌ failure
vuetify	✅ success	✅ success
vueuse	✅ success	✅ success
router	✅ success	✅ success
language-tools	✅ success	✅ success
nuxt	✅ success	✅ success

fix(watch): trigger immediate callback for empty sources

a7b2f62

chore: update test

a6f8783

edison1105 added ready to merge The PR is ready to be merged. 🍰 p2-nice-to-have Priority 2: this is not breaking anything but nice to have it addressed. labels Jun 4, 2026

edison1105 mentioned this pull request Jun 6, 2026

fix(reactivity): trigger immediate watch for empty sources #14928

Closed

edison1105 merged commit 1f2ca7e into vuejs:main Jun 11, 2026
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fix(watch): trigger immediate callback for empty sources (fix #14898)#14914

fix(watch): trigger immediate callback for empty sources (fix #14898)#14914
edison1105 merged 2 commits into
vuejs:mainfrom
puneetdixit200:fix-empty-array-immediate-watch

puneetdixit200 commented Jun 4, 2026 •

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