How to use Provide/Inject in Vue.js with TypeScript

You provide anything you want from a higher component by using the @Provide decorator, and then ask for it in a lower component by using @Inject. For example:

In the parent component, you provide the value using @Provide(<someKey>)

//Parent.vue
<template>
  <div>The parents value: {{this.providedValue}}</div>
  <child />
</template>

<script lang="ts">
  import { Component, Vue, Provide} from 'vue-property-decorator';
  import Child from './Child.vue';

  @Component({components: Child})
  export default class Parent extends Vue {
    @Provide('key') private providedValue: string = 'The value';
  }
</script>

Now we've declared a value with the name key that can be consumed by all children, multiple levels deep:

//Child.vue
<template>
  <div>The childs value: {{this.injectedValue}}</div>
</template>

<script lang="ts">
  import { Component, Vue, Inject } from 'vue-property-decorator';

  @Component
  export default class Child extends Vue {
    @Inject('key') private injectedValue!: string;
  }
</script>

The property injectedValue will now be injected by Vue by walking up on the hierarchy until it finds a provided value with the key key.

If you want something dependency injection-like, it's best to provide the value at the top, where you create your Vue instance:

//index.ts
import Vue from 'vue';
//... imports and configs
new Vue({
  el: '#app',
  // Provide values by returning a key-value pair
  provide: () => ({
    'key1': 'value1',
    'key2': 'value2'
  }),
  render: h => h(App)
});

Now you can use @Inject('key1') in any component of this Vue instance.

You may use vue 3 and class style component, then you have to define provider/inject by this way:

in vue 3 except Component annotation there is Options annotation and we use it to define provide/inject parameters. More info

// Parent component
import { Vue, Options } from "vue-class-component";
import { computed } from "@vue/reactivity";

@Options({
  provide: {
    staticParameter: 'static value',
    reactiveParameter: computed(() => 'Normal computed value'),
  },
})
export default class ParentComponent extends Vue {}

// Child component
import { Vue, Options } from "vue-class-component";

@Options({
  inject: ["staticParameter", "reactiveParameter"],
})
export default class Timer extends Vue {
  staticParameter!: string;
  reactiveParameter!:string
}