npm install --save-dev typescript
npm install --save-dev @vue/cli-plugin-typescript

{
 "compilerOptions": {
  "target": "esnext",
  "module": "esnext",
  "strict": true,
  "importHelpers": true,
  "moduleResolution": "node",
  "experimentalDecorators": true,
  "esModuleInterop": true,
  "allowSyntheticDefaultImports": true,
  "sourceMap": true,
  "baseUrl": ".",
  "allowJs": false,
  "noEmit": true,
  "types": [
   "webpack-env"
  ],
  "paths": {
   "@/*": [
    "src/*"
   ]
  },
  "lib": [
   "esnext",
   "dom",
   "dom.iterable",
   "scripthost"
  ]
 },
 "exclude": [
  "node_modules"
 ]
}

declare module '*.vue' {
 import Vue from 'vue'
 export default Vue
}

src/main.js => src/main.ts

// 加上 lang=ts 让webpack识别此段代码为 typescript
<script lang="ts">
 import Vue from 'vue'
 export default Vue.extend({
  // ...
 })
</script>

import Vue from 'vue'
import Component from 'vue-class-component'

// 表明此组件接受propMessage参数
@Component({
  props: {
    propMessage: String
  }
})
export default class App extends Vue {
  // 等价于 data() { return { msg: 'hello' } }
  msg = 'hello';
  
  // 等价于是 computed: { computedMsg() {} }
  get computedMsg() {
    return 'computed ' + this.msg
  }
  
  // 等价于 methods: { great() {} }
  great() {
    console.log(this.computedMsg())
  }
}

import { Vue, Component, Prop, Watch, Emit } from 'vue-property-decorator'

@Component
export default class App extends Vue {
  @Prop(Number) readonly propA: Number | undefined
  @Prop({ type: String, default: ''}) readonly propB: String
  
  // 等价于 watch: { propA(val, oldval) { ... } }
  @Watch('propA')
  onPropAChanged(val: String, oldVal: String) {
    // ...
  }
  
  // 等价于 resetCount() { ... this.$emit('reset') }
  @Emit('reset')
  resetCount() {
    this.count = 0
  }
  
  // 等价于 returnValue() { this.$emit('return-value', 10, e) }
  @Emit()
  returnValue(e) {
    return 10
  }
  
  // 等价于 promise() { ... promise.then(value => this.$emit('promise', value)) }
  @Emit()
  promise() {
    return new Promise(resolve => {
      resolve(20)
    })
  }
}