Difference between "v-bind:value" and "v-bind:key" in vue js

Question

Below is my code. I want to use "select" tag and I want to render the options and its value from the script. I have used "v-bind:value" for rendering the values from the script. But there is an error such as ***"

[eslint-plugin-vue] [vue/require-v-for-key] Elements in iteration expect to have 'v-bind:key'

directives."***

Hence I have given like this **"

< option v-for= "option in nationalityOpt" v-bind:value="option.value" v-bind:key = ""> {{ option.text }} < / option> ".

If I removed the "v-bind:value" from my code then I could not get the option values in the UI. I want to rectify the error for "v-bind:key" and I would like to know the difference between those two. Please help.

<template>
 <b-card>
    <h4 slot="header" class="card-title">Employee</h4>
        <b-row>
            <b-col sm="3">
              <b-form-group>
                <label for="name">First Name </label>
                <input type="text" id="name"  class="form-control" placeholder="Enter your name" v-model="firstName">
               </b-form-group>
            </b-col>
     </b-row>
      <b-row>
            <b-col sm="3">
              <b-form-group>
                <label for="name">Nationality</label>
                <select name="" id="" class="form-control"  placeholder="Nationality" v-model="nationality">
                  <option v-for="option in nationalityOpt" v-bind:value="option.value"> {{ option.text }} </option>
                </select>
              </b-form-group>
            </b-col>
          </b-row>
      <input type="submit" value="Submit" @click="validateForm">
 </b-card>
</template>

<script>
export default {
  name: 'addEmpl',
  data () {
    return {
      firstName: '',
      nationality: '1',
      nationalityOpt: [
        { value: '1', text: 'Select' },
        { value: 'IN', text: 'Indian'},
        { value: 'OT', text: 'Others'}
        ],
    }
  }
}
</script>

Thanks in advance.

Answer 1

Check the docs for List Rendering, specifically about the keys.

You need the v-bind:key in a v-for because it needs to differentiate each component rendered, in case of data changing. You need to use the both, v-bind:key and v-bind:value in your component option, to make it work as you expect.

You can simplify and use just :key and :value, like:

<option v-for="option in nationalityOpt" :value="option.value" :key="option.value"> 
    {{ option.text }}
</option>

Answer 2

Vue.js has some methods to increase rendering efficiency by reusing component. To make the list (with v-for) render correctly, we should provide unique :key binding to each element https://v2.vuejs.org/v2/guide/list.html#key

 <select name="" id="" class="form-control"  placeholder="Nationality" v-model="nationality">
       <option v-for="option in nationalityOpt" v-bind:value="option.value" :key="option.value"> {{ option.text }} </option>
    </select>