JS箭头函数

箭头函数的作用域是和定义这个箭头函数的父级上下文绑定在一起的
匿名函数的作用域是和定义匿名函数的上下文绑定在一起的

luke = {
    id: 2,
    say: function() {
        setTimeout(function() {
            console.log(this.id)
        }, 50)
    },
    sayWithThat: function() {
        let that = this
        setTimeout(function() {
            console.log(that.id)
        }, 50)
    },
    sayWithArrow: function() {
        setTimeout(() => {
            console.log(this.id)
        }, 50)
    },
    sayWithGlobalArrow: () => {
        setTimeout(() => {
            console.log(this.id)
        }, 50);
    }
}

luke.say()
luke.sayWithThat()
luke.sayWithArrow()
luke.sayWithGlobalArrow()

有了箭头函数，再也不用写that这种hack