class CancelToken {

  reason = ''

  constructor(executor) {

    console.log('executor = ', executor)

    executor(message => {

      console.log('message', message)

      if (this.reason) return

​

      this.reason = message

    })

  }

}

​

let cancel;

​

function fn(c){

  console.log('c = ', c)

  cancel = c

}

​

function fn2(message) {

  console.log('message', message)

  if (this.reason) return

​

  this.reason = message

}

​

// new CancelToken(fn)

​

// cancel()

​

fn(fn2) // 注意此时 fn2 并没有被调用

​

// fn2 什么时候才会被调用? 因为 c === fn2

// 只有当 c 调用，fn2 才会被调用

​

cancel()

​