JS彈幕實作

基于直播平台的流行，利用原生實作一下彈幕效果。

原文連結

實作原理

1、設定展示彈幕元素位置屬性為relative

2、動态建立彈幕元素，位置屬性設定absolute，left為展示寬度

3、随機設定彈幕元素top值

4、随機産生彈幕元素移動速率，修改left值

随機顔色

第一種實作
let color = '#' + Math.floor(Math.random() * 0xffffff).toString(16);

第二種實作
let color = '#' + Math.floor(Math.random() * 16777215).toString(16);

第三種實作
let r = Math.floor(Math.random()*256);
let g = Math.floor(Math.random()*256);
let b = Math.floor(Math.random()*256);
let color = `rgb(${r},${g},${b})`;
           

随機速率

50 * +Math.random().toFixed(2)
           

代碼

//html
<div class="container">
    <div id="content" class="content"></div>
    <div class="content-opt">
        <div id="content-text" class="content-text"></div>
        <div class="content-input">
            <input id="text" type="text">
            <button id="send">發送</button>
        </div>
    </div>
</div>

//css
* {
    box-sizing: border-box;
    outline: none;
}

p {
    margin: .5em;
    word-break: break-all;
}

.container {
    position: relative;
    width: 700px;
    height: 500px;
    margin: auto;
    padding-right: 200px;
}

.content {
    width: 100%;
    height: 100%;
    border: 1px solid #ccc;
}

.content-opt {
    position: absolute;
    top: 0;
    right: 0;
    width: 200px;
    height: 100%;
}

.content-text {
    height: calc(100% - 30px);
    margin-bottom: 30px;
    border: 1px solid #ccc;
    overflow: auto;
}

.content-input {
    position: absolute;
    bottom: 0;
    width: 100%;
    height: 30px;
    border: 1px solid #ccc;
}

.content-input input {
    width: 70%;
    padding: 2px;
    border-radius: 5px;
}

.content-input button {
    padding: 3px 10px;
    border: none;
    border-radius: 5px;
    background: rgb(90, 154, 214);
}

//js
(function () {
    class Barrage {
        constructor(id) {
            this.domList = [];
            this.dom = document.querySelector('#' + id);
            if (this.dom.style.position == '' || this.dom.style.position == 'static') {
                this.dom.style.position = 'relative';
            }
            this.dom.style.overflow = 'hidden';
            let rect = this.dom.getBoundingClientRect();
            this.domWidth = rect.right - rect.left;
            this.domHeight = rect.bottom - rect.top;
        }

        shoot(text) {
            let div = document.createElement('div');
            div.style.position = 'absolute';
            div.style.left = this.domWidth + 'px';
            div.style.top = (this.domHeight - 20) * +Math.random().toFixed(2) + 'px';
            div.style.whiteSpace = 'nowrap';
            div.style.color = '#' + Math.floor(Math.random() * 256).toString(10);
            div.innerText = text;
            this.dom.appendChild(div);

            let roll = (timer) => {
                let now = +new Date();
                roll.last = roll.last || now;
                roll.timer = roll.timer || timer;
                let left = div.offsetLeft;
                let rect = div.getBoundingClientRect();
                if (left < (rect.left - rect.right)) {
                    this.dom.removeChild(div);
                } else {
                    if (now - roll.last >= roll.timer) {
                        roll.last = now;
                        left -= 3;
                        div.style.left = left + 'px';
                    }
                    requestAnimationFrame(roll);
                }
            }
            roll(50 * +Math.random().toFixed(2));
        }

    }

    let barage = new Barrage('content');

    function appendList(text) {
        let p = document.createElement('p');
        p.innerText = text;
        document.querySelector('#content-text').appendChild(p);
    }

    document.querySelector('#send').onclick = () => {
        let text = document.querySelector('#text').value;
        barage.shoot(text);

        appendList(text);
    };

    const textList = ['彈幕', '666', '233333333', 'javascript', 'html', 'css', '前端架構', 'Vue', 'React', 'Angular',
        '測試彈幕效果'
    ];
    textList.forEach((s) => {
        barage.shoot(s);
        appendList(s);
    })
})()
           

效果