Why shouldn't we use :key="index" in v-for #94

xianshenglu · 2019-05-30T11:43:05Z

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <meta http-equiv="X-UA-Compatible" content="ie=edge" />
    <title>Document</title>
    <link
      rel="stylesheet"
      href="https://unpkg.com/element-ui/lib/theme-chalk/index.css"
    />
    <style>
      * {
        margin: 0;
        padding: 0;
      }
      .app {
        width: 90vh;
        height: 80vh;
        padding: 15px;
        background: #eee;
        margin: 10vh auto;
        overflow: auto;
      }
      .app__button {
        margin: 0 auto;
      }
      .app__checkbox {
        margin: 10px;
        display: block;
      }
    </style>
  </head>
  <body>
    <script src="https://cdn.jsdelivr.net/npm/[email protected]/dist/vue.js"></script>
    <script src="https://cdn.jsdelivr.net/npm/[email protected]/lib/index.js"></script>
    <div id="app" class="app">
      <el-button class="app__button" @click="unshiftOption"
        >unshiftOption
      </el-button>
      <el-checkbox
        class="app__checkbox"
        v-for="(item,index) in options"
        :key="index"
        v-model="item.checked"
        >{{ item.label }}</el-checkbox
      >
    </div>
    <script>
      new Vue({
        el: '#app',
        data: {
          value: '',
          options: [
            { label: 'label1', name: 'checkbox1', checked: undefined },
            { label: 'label2', name: 'checkbox2', checked: undefined },
            { label: 'label3', name: 'checkbox3', checked: undefined }
          ],
          counter: 4
        },
        created() {
          window.vm = this
        },
        methods: {
          unshiftOption() {
            const count = this.counter++
            this.options.unshift({
              label: 'label' + count,
              name: 'checkbox' + count,
              checked: undefined
            })
          }
        }
      })
    </script>
  </body>
</html>

demo2

In this case, append a new item doesn't run the data function. So, it shows the wrong value. Normally, it should run the data function to get a new state.

Solution

Bind key to unique id would solve this problem. For example, in demo1 we can

:key="name"

And in demo2, we can

:key="i"

Performance

todo....

Reference

The text was updated successfully, but these errors were encountered:

xianshenglu changed the title ~~Why not using :key="index"~~ Why not using :key="index" in v-for May 30, 2019

xianshenglu changed the title ~~Why not using :key="index" in v-for~~ Why shouldn't we use :key="index" in v-for May 30, 2019

xianshenglu added edge-case framework-specific labels Aug 14, 2023

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Why shouldn't we use :key="index" in v-for #94

Why shouldn't we use :key="index" in v-for #94

xianshenglu commented May 30, 2019 •

edited

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Why shouldn't we use :key="index" in v-for #94

Why shouldn't we use :key="index" in v-for #94

Comments

xianshenglu commented May 30, 2019 • edited Loading

Solution

Performance

Reference

xianshenglu commented May 30, 2019 •

edited

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