How to pass TypeScript constants to Vue templates with least amount of reactivity

Question

I'm wondering what's the most performant way to pass a constant to a template. Currently, I'm using data, but as far as I understand, that should be mostly used for state that changes over time and Vue adds event listeners to the data. The constants are just that - constant values that are used for output in templates, they'll never change during the lifetime of the app.

<template>
  <div>
   <input type="radio" name="color" :value=Colors.GREEN />
   <input type="radio" name="color" :value=Colors.RED />
  </div>
</template>
<script lang="ts">
import Vue from 'vue';
import Colors from '@/viewmodels/colors';

export default Vue.extend({
    name: 'ExampleComponent',
    data() {
        return () => {
            Colors
        }
    }
})
</script>

Possible duplicate of [How could I use const in vue template?](https://stackoverflow.com/questions/42662144/how-could-i-use-const-in-vue-template) — Etheryte, May 13 '19 at 16:21

tao · Accepted Answer · 2019-05-14T09:40:11.350

The decision is based on whether or not the value of Colors will change throughout the lifecycle of your component. If it won't change, simply use a computed property:

Vue.config.devtools = false;
Vue.config.productionTip = false;

const Colors = {
  GREEN: '#0F0',
};
Vue.component('ExampleComponent', {
  name: 'ExampleComponent',
  template: `
    <div>
      Value: <span style="color:${Colors.GREEN}">{{ Colors.GREEN }}</span>
    </div>
  `,
  computed: {
    Colors: () => Colors
  }
})
new Vue({
  el: '#app',
})

<script src="https://cdnjs.cloudflare.com/ajax/libs/vue/2.5.17/vue.js"></script>

<div id="app">
  <example-component />
</div>

If you plan on changing it (based on user interaction or script), place it in data():

Vue.config.devtools = false;
Vue.config.productionTip = false;

const Colors = {
  GREEN: '#0F0',
};
Vue.component('ExampleComponent', {
  name: 'ExampleComponent',
  template: `
    <div>
      Value: <span :style="{color: Colors.GREEN}">{{ Colors.GREEN }}</span>
      <button @click="changeColors">Change Colors</button>
    </div>
  `,
  data: () => ({
    Colors
  }),
  methods: {
    changeColors() {
      this.Colors = {
        GREEN: 'red'
      }
    }
  }
})
new Vue({
  el: '#app',
})

<script src="https://cdnjs.cloudflare.com/ajax/libs/vue/2.5.17/vue.js"></script>

<div id="app">
  <example-component />
</div>

If you want to allow the user to select one of the available options in Colors, it means Colors contents won't change, therefore you'll use a computed for Colors, along with a data() for currently selected color:

Vue.config.devtools = false;
Vue.config.productionTip = false;

const Colors = {
  GREEN: '#090',
  RED: '#C00',
  BLUE: '#009',
  ORANGE: '#F90'
};
Vue.component('ExampleComponent', {
  name: 'ExampleComponent',
  template: `
    <div> Value:
      <span 
        :style="{color: currentColor, fontWeight: 'bold'}"
        v-text="currentColor" />
      <select v-model="currentColor">
         <option 
           v-for="(color, key) of Colors"
           v-text="\`\${key}: \${color}\`"
           :key="key"
           :value="color" />
       </select>
    </div>
  `,
  data: () => ({
    currentColor: Colors.GREEN
  }),
  computed: {
    Colors: () => Colors
  },
  methods: {
    setColor(color) {
      this.currentColor = color;
    }
  }
})
new Vue({
  el: '#app',
})

<script src="https://cdnjs.cloudflare.com/ajax/libs/vue/2.5.17/vue.js"></script>

<div id="app">
  <example-component />
</div>

You've updated your question with checkboxes. So I added an example using both checkboxes and radios, depending on what one might need:

Vue.config.devtools = false;
Vue.config.productionTip = false;

const Colors = {
  GREEN: '#090',
  RED: '#C00',
  BLUE: '#009',
  ORANGE: '#F90'
};
Vue.component('ExampleComponent', {
  name: 'ExampleComponent',
  template: `
    <div> checkedColors:
      <label v-for="(color, key) of Colors"
             :key="key">
        <input name="color"
               type="checkbox"
               :value="color"
               v-model="checkedArray">
        <span v-text="color" :style="{color}" />
      </label>
      <hr>
      pickedColor: 
      <label v-for="(color, key) of Colors"
             :key="color">
        <input name="picked"
               type="radio"
               :value="color"
               v-model="picked">
        <span v-text="color" :style="{color}" />
      </label>
      <hr>
      <pre>checkedArray: {{ stringify(checkedArray) }}</pre>
      <pre>picked: {{ picked }}</pre>
    </div>
  `,
  data: () => ({
    checkedArray: [],
    picked: Colors.GREEN
  }),
  computed: {
    Colors: () => Colors
  },
  methods: {
    stringify(value) {
      return JSON.stringify(value, true, 2);
    }
  }
})
new Vue({
  el: '#app',
})

<script src="https://cdnjs.cloudflare.com/ajax/libs/vue/2.5.17/vue.js"></script>

<div id="app">
  <example-component />
</div>

How to pass TypeScript constants to Vue templates with least amount of reactivity

1 Answers1