[Vuejs]-How to include promises in vuejs methods

The problem is with the if (this.done) check.
When done is false, the promise is never resolved, and the handleStart never receives data.

If you need to react when a data has changed, take a look Vue’s watchers

you need to use watchers to watch this.done change

watch: {
  done(newVal, oldVal) {
    if (newVal) {
      // do something
    }
  }
}, 
methods: {
  async handleStart () {
    // how to make this async
    this.start = true
    const data = await this.foo()
    console.log("I must be printed with:", data))
  }
}