原生JavaScript实现弹幕组件的示例代码原生JavaScript实现弹幕组件的示

前言

如今几乎所有的视频网站都有弹幕功能，那么今天我们就自己用原生 JavaScript 封装一个弹幕类。这个类希望有如下属性和实例方法：

属性

el容器节点的选择器，容器节点应为绝对定位，设置好宽高
height 每条弹幕的高度
mode 弹幕模式，half则为一半容器高度，top为三分之一，full为占满
speed弹幕划过屏幕的时间
gapWidth后一条弹幕与前一条弹幕的距离

方法

pushData 添加弹幕元数据
addData持续加入弹幕
start开始调度弹幕
stop停止弹幕
restart 重新开始弹幕
clearData清空弹幕
close关闭
open重新显示弹幕

PS:有一些自封装的工具函数就不贴出来了，大概知道意思就好
初始化

引入JavaScript文件之后，我们希望如下使用，先采取默认配置。

let barrage = new Barrage({el: '#container'})

参数初始化：

function Barrage(options) {let {el,height,mode,speed,gapWidth,} = optionsthis.container = document.querySelector(el)this.height = height || 30this.speed = speed || 15000 //2000msthis.gapWidth = gapWidth || 20this.list = []this.mode = mode || 'half'this.boxSize = getBoxSize(this.container)this.perSpeed = Math.round(this.boxSize.width / this.speed)this.rows = initRows(this.boxSize, this.mode, this.height)this.timeoutFuncs = []this.indexs = []this.idMap = []}

先接受好参数然后初始化，下面看看getBoxSize和initRows

function getBoxSize(box) {let {height,width} = window.getComputedStyle(box)return {height: px2num(height),width: px2num(width)}function px2num(str) {return Number(str.substring(0, str.indexOf('p')))}}

通过getComputedStyleapi计算出盒子的宽高，这里用来计算容器的宽高，之后也会用到。

function initRows(box, mode, height) {let divisor = getDivisor(mode)rows = Math.ceil(box.height * divisor / height)return rows}function getDivisor(mode) {let divisor = .5switch (mode) {case 'half':divisor = .5breakcase 'top':divisor = 1 / 3break; case 'full':divisor = 1; breakdefault:break; }return divisor}

根据高度算出弹幕应该有多少行，下面会有地方用到行数。

插入数据

有两种插入数据的方法，一种是添加源数据，一种是持续添加。先来看添加源数据的方法：

this.pushData = https://www.it610.com/article/function (data) {this.initDom()if (getType(data) =='[object Object]') {//插入单条this.pushOne(data)}if (getType(data) == '[object Array]') {//插入多条this.pushArr(data)}}

this.initDom = function () {if (!document.querySelector(`${el} .barrage-list`)) {//注册dom节点for (let i = 0; i < this.rows; i++) {let div = document.createElement('div')div.classList = `barrage-list barrage-list-${i}`div.style.height = `${this.boxSize.height*getDivisor(this.mode)/this.rows}px`this.container.appendChild(div)}}}this.pushOne = function (data) {for (let i = 0; i < this.rows; i++) {if (!this.list[i]) this.list[i] = []}let leastRow = getLeastRow(this.list) //获取弹幕列表中最少的那一列，弹幕列表是一个二维数组this.list[leastRow].push(data)}this.pushArr = function (data) {let list = sliceRowList(this.rows, data)list.forEach((item, index) => {if (this.list[index]) {this.list[index] = this.list[index].concat(...item)} else {this.list[index] = item}})}//根据行数把一维的弹幕list切分成rows行的二维数组function sliceRowList(rows, list) {let sliceList = [],perNum = Math.round(list.length / rows)for (let i = 0; i < rows; i++) {let arr = []if (i == rows - 1) {arr = list.slice(i * perNum)} else {i == 0 ? arr = list.slice(0, perNum) : arr = list.slice(i * perNum, (i + 1) * perNum)}sliceList.push(arr)}return sliceList}

持续加入数据的方法只是调用了添加源数据的方法，并且开始了调度而已

this.addData = https://www.it610.com/article/function (data) {this.pushData(data)this.start()}

发射弹幕

下面来看看发射弹幕的逻辑

this.start = function () {//开始调度listthis.dispatchList(this.list)}this.dispatchList = function (list) {for (let i = 0; i < list.length; i++) {this.dispatchRow(list[i], i)}}this.dispatchRow = function (row, i) {if (!this.indexs[i] && this.indexs[i] !== 0) {this.indexs[i] = 0}//真正的调度从这里开始，用一个实例变量存储好当前调度的下标。if (row[this.indexs[i]]) {this.dispatchItem(row[this.indexs[i]], i, this.indexs[i])}}

this.dispatchItem = function (item, i) {//调度过一次的某条弹幕下一次在调度就不需要了if (!item || this.idMap[item.id]) {return}let index = this.indexs[i]this.idMap[item.id] = item.idlet div = document.createElement('div'),parent = document.querySelector(`${el} .barrage-list-${i}`),width,pastTimediv.innerHTML = item.contentdiv.className = 'barrage-item'parent.appendChild(div)width = getBoxSize(div).widthdiv.style = `width:${width}px; display:none`pastTime = this.computeTime(width) //计算出下一条弹幕应该出现的时间//弹幕飞一会~this.run(div)if (index > this.list[i].length - 1) {return}let len = this.timeoutFuncs.length//记录好定时器，后面清空this.timeoutFuncs[len] = setTimeout(() => {this.indexs[i] = index + 1//递归调用下一条this.dispatchItem(this.list[i][index + 1], i, index + 1)}, pastTime); }

//用css动画，整体还是比较流畅的this.run = function (item) {item.classList += ' running'item.style.left = "left:100%"item.style.display = ''item.style.animation = `run ${this.speed/1000}s linear`//已完成的打一个标记setTimeout(() => {item.classList+=' done'}, this.speed); }//根据弹幕的宽度和gapWth，算出下一条弹幕应该出现的时间this.computeTime = function (width) {let length = width + this.gapWidthlet time = Math.round(length / this.boxSize.width * this.speed/2)return time}

动画css具体如下

@keyframes run {0% {left: 100%; }50% {left: 0}100% {left: -100%; }}.run {animation-name: run; }

其余方法

停止

利用动画的paused属性停止

this.stop = function () {let items = document.querySelectorAll(`${el} .barrage-item`); [...items].forEach(item => {item.className += ' pause'})}

.pause {animation-play-state: paused !important; }

重新开始

移除pause类即可

this.restart = function () {let items = document.querySelectorAll(`${el} .barrage-item`); [...items].forEach(item => {removeClassName(item, 'pause')})}

打开关闭

做一个显示隐藏的逻辑即可

this.close = function () {this.container.style.display = 'none'}this.open = function () {this.container.style.display = ''}

清理弹幕

this.clearData = https://www.it610.com/article/function () {//清除listthis.list = []//清除domdocument.querySelector(`${el}`).innerHTML =''//清除timeoutthis.timeoutFuncs.forEach(fun => clearTimeout(fun))}

最后用一个定时器定时清理过期的弹幕:

setInterval(() => {let items = document.querySelectorAll(`${el} .done`); [...items].forEach(item=>{item.parentNode.removeChild(item)})}, this.speed*5);

最后

感觉这个的实现还是有缺陷的，如果是你设计这么一个类，你会怎么设计呢？
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