js实现动态球球背景

document.getElementsByTagName("body")[0].style.backgroundColor="#000"
    //构造函数
    function Ball( size, left1, top1, color, step, directionLeft, directionTop, timeSpace,opc){
        this.dom = null
        this.size = size
        this.left1 = left1
        this.top1 = top1
        this.color = color
        this.step = step
        this.timeSpace = timeSpace
        this.directionLeft = directionLeft
        this.directionTop = directionTop
        this.opc = opc
        //创建球
        this.createDom = function(){
            this.dom = document.createElement("div")
            this.dom.style.cssText = `
                position: absolute;
                left: ${this.left1}px;
                top: ${this.top1}px;
                width: ${this.size}px;
                height: ${this.size}px;
                border-radius: 50%;
                background-color:${this.color};
                opacity: ${this.opc};
                z-index: -999999999;
            `;
            document.body.appendChild(this.dom)//吧效果加到body;里面
        }

        //球的动作
        this.go = function () {
            setInterval(() => {
                this.left1 = this.left1 + this.directionLeft * this.step
                this.top1 = this.top1 + this.directionTop * this.step

                // 边界判断
                let clientHeigth = document.documentElement.clientHeight || document.body.clientHeight
                let scrollTop = document.documentElement.scrollTop || document.body.scrollTop
                if (this.top1 + this.size > clientHeigth + scrollTop) {
                    this.top1 = clientHeigth + scrollTop - this.size
                    this.directionTop = -1
                } else if (this.top1 < scrollTop) {
                    this.top1 = scrollTop
                    this.directionTop = 1
                }
                let clientWidth = document.documentElement.clientWidth || document.body.clientWidth
                let scrollLeft = document.documentElement.scrollLeft || document.body.scrollLeft
                if (this.left1 + this.size > clientWidth + scrollLeft) {
                    // 右边界
                    this.left1 = clientWidth + scrollLeft - this.size
                    this.directionLeft = -1
                } else if (this.left1 < scrollLeft) {
                    //左边界
                    this.left1 = scrollLeft
                    this.directionLeft = 1
                }

                this.dom.style.left = this.left1 + "px"
                this.dom.style.top = this.top1 + "px"
            }, this.timeSpace)
        }
        //调用
        this.createDom()
        this.go()
    } 

    window.onload = function () {
        var w = document.documentElement.clientWidth||document.body.clientWidth
        var h =document.documentElement.clientHeight||document.body.clientHeight
        for(var i=0;i<200;i++){
            // 随机大小(10-150)
            let size = parseInt(Math.random()*141)+10
            // 随机位置；
            let left1 = parseInt(Math.random()*w)
            let top1 = parseInt(Math.random()*h)
            // 随机颜色
            let color = getColor()
            // 随机步长(1-10)
            let step = parseInt(Math.random()*5)+1
            // 随机方向
            let directionLeft = parseInt(Math.random()*2)==0?-1:1 //0和1
            let directionTop = parseInt(Math.random()*2)==0?-1:1 //0和1
            // 随机时间间隔(5-50)
            let timeSpace = parseInt(Math.random()*46)+5
            //透明度
            let opc = (parseInt(Math.random()*6)+1)/10

            new Ball( size, left1, top1, color, step, directionLeft, directionTop, timeSpace,opc)
        }
    }
    function getColor(){//随机颜色
        var str = "#"
        for(var i=0;i<6;i++){
            str += parseInt(Math.random()*16).toString(16)
        }
        return str
    }