原生js改变背景色

   function Color(elem) {
        this.elem = elem
        this.Colors = ['#1abc9a', '#4ddbac', '#ccc9a9', '#6ab39a', '#5cdc9a']
        this.run = function () {
            setInterval(function () {
                let i =  Math.floor(Math.random()*this.Colors.length)  
                // console.log(i) 随机数
                this.elem.style.backgroundColor = this.Colors[i] //改变颜色
            }.bind(this)
                , 1000)
        }
    }
    let obj = new Color(document.body)
    obj.run()