原生JavaScript实现弹幕组件

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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,
    } = options
    this.container = document.querySelector(el)
    this.height = height || 30
    this.speed = speed || 15000 //2000ms
    this.gapWidth = gapWidth || 20
    this.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getBoxSizeinitRows

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 = .5
    switch (mode) {
        case 'half':
            divisor = .5
            break
        case 'top':
            divisor = 1 / 3
            break;
        case 'full':
            divisor = 1;
            break
        default:
            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 = 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 = 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list
    this.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.id
    let div = document.createElement('div'),
        parent = document.querySelector(`${el} .barrage-list-${i}`),
        width,
        pastTime
    div.innerHTML = item.content
    div.className = 'barrage-item'
    parent.appendChild(div)
    width = getBoxSize(div).width
    div.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.gapWidth
    let 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 = function () {
    //清除list
    this.list = []
    //清除dom
    document.querySelector(`${el}`).innerHTML = ''
    //清除timeout
    this.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?