SOURCE

var id = 11;

function fn2(){
    this.id = 1;
    setTimeout(function(){
        console.log(this.id);
        console.log(this.id2)
    }, 150);
    setTimeout(() => {
        console.log(this.id);
        console.log(this.id2);
    }, 200)
}

fn2.call({id2: 33});

function Timer() {
  this.s1 = 0;
  this.s2 = 0;
  // 箭头函数
  setInterval(() => this.s1++, 1000);
  // 普通函数
  setInterval(function () {
    this.s2++;
  }, 1000);
}

var timer = new Timer();

setTimeout(() => console.log('s1: ', timer.s1), 3100);
setTimeout(() => console.log('s2: ', timer.s2), 3100);