Version

3.0.4

Reproduction link

https://gitee.com/liguangzheng777/school/blob/master/src/views/student/add.vue

Steps to reproduce

<!-- html -->
<el-option v-for="(item, i) in state.classesArr" :key="i" :label="item.name" :value="item.name"> </el-option>

// js
const state = reactive({classesArr: []})

onBeforeMount(() => {
      state.classesArr = [0,1,2]
})

console: Uncaught (in promise) TypeError: oldChildren is null

if : const state = reactive({classesArr: [0]})

code run success

What is expected?

lgz

What is actually happening?

[] is null?? how to solve

how to solve,thanks

You overwirte the value at here https://gitee.com/liguangzheng777/school/blob/master/src/views/student/add.vue#L97

You overwirte the value at here https://gitee.com/liguangzheng777/school/blob/master/src/views/student/add.vue#L97

in 97 overwirte console error:Uncaught (in promise) TypeError: oldChildren is null I attempt shield https://gitee.com/liguangzheng777/school/blob/master/src/views/student/add.vue#L26 code success

You overwirte the value at here https://gitee.com/liguangzheng777/school/blob/master/src/views/student/add.vue#L97

in 97 overwirte console error:Uncaught (in promise) TypeError: oldChildren is null I attempt shield https://gitee.com/liguangzheng777/school/blob/master/src/views/student/add.vue#L26 code success

in 97 overwirte console: Uncaught (in promise) TypeError: oldChildren is null patchBlockChildren runtime-dom.esm-bundler-f3a18650.js:5142 processFragment runtime-dom.esm-bundler-f3a18650.js:5211 patch runtime-dom.esm-bundler-f3a18650.js:4854 patchBlockChildren runtime-dom.esm-bundler-f3a18650.js:5159 patchElement runtime-dom.esm-bundler-f3a18650.js:5123 processElement runtime-dom.esm-bundler-f3a18650.js:4941 patch runtime-dom.esm-bundler-f3a18650.js:4858 patchBlockChildren runtime-dom.esm-bundler-f3a18650.js:5159 patchElement runtime-dom.esm-bundler-f3a18650.js:5123 processElement runtime-dom.esm-bundler-f3a18650.js:4941 patch runtime-dom.esm-bundler-f3a18650.js:4858 componentEffect runtime-dom.esm-bundler-f3a18650.js:5421 reactiveEffect runtime-dom.esm-bundler-f3a18650.js:339 callWithErrorHandling runtime-dom.esm-bundler-f3a18650.js:1300 flushJobs runtime-dom.esm-bundler-f3a18650.js:1508 promise callbackqueueFlush runtime-dom.esm-bundler-f3a18650.js:1410 queueJob runtime-dom.esm-bundler-f3a18650.js:1404 run runtime-dom.esm-bundler-f3a18650.js:480 trigger runtime-dom.esm-bundler-f3a18650.js:486 set runtime-dom.esm-bundler-f3a18650.js:588 classes2 \a\vue3\handbook\src\views\student\add.vue:97 setup \a\vue3\handbook\src\views\student\add.vue:88 callWithErrorHandling runtime-dom.esm-bundler-f3a18650.js:1300 callWithAsyncErrorHandling runtime-dom.esm-bundler-f3a18650.js:1309 __weh runtime-dom.esm-bundler-f3a18650.js:3056 flushPostFlushCbs runtime-dom.esm-bundler-f3a18650.js:1479 flushJobs runtime-dom.esm-bundler-f3a18650.js:1515 promise callbackqueueFlush runtime-dom.esm-bundler-f3a18650.js:1410 queueCb runtime-dom.esm-bundler-f3a18650.js:1432 queuePostFlushCb runtime-dom.esm-bundler-f3a18650.js:1438 queueEffectWithSuspense runtime-dom.esm-bundler-f3a18650.js:2530 scheduler runtime-dom.esm-bundler-f3a18650.js:3217 run runtime-dom.esm-bundler-f3a18650.js:480 trigger runtime-dom.esm-bundler-f3a18650.js:486 scheduler runtime-dom.esm-bundler-f3a18650.js:1116 run runtime-dom.esm-bundler-f3a18650.js:480 trigger runtime-dom.esm-bundler-f3a18650.js:486 scheduler runtime-dom.esm-bundler-f3a18650.js:1116 run runtime-dom.esm-bundler-f3a18650.js:480 trigger runtime-dom.esm-bundler-f3a18650.js:486 set value runtime-dom.esm-bundler-f3a18650.js:1026 finalizeNavigation vue-router.esm-bundler.js:2585 pushWithRedirect vue-router.esm-bundler.js:2458 promise callback*pushWithRedirect vue-router.esm-bundler.js:2429 push vue-router.esm-bundler.js:2369 install vue-router.esm-bundler.js:2727 use runtime-dom.esm-bundler-f3a18650.js:4094 \a\vue3\handbook\src\main.ts:16

@underfin why this array default cannot set [] , only set [0],[{}] and more ? because this array render el-option ?

@underfin why this array default cannot set [] , only set [0],[{}] and more ? because this array render el-option ?

to be exact , this array default set [] , overwrite will be error , but default set [0],[{}] will not error

Duplicate of https://github.com/vuejs/vue-next/issues/2820

When opening bug reports make sure to follow https://new-issue.vuejs.org/?repo=vuejs/vue#why-repro

Oh.Sorry for mistaken.