基于JavaScript实现新年贺卡特效

动图演示

一款超级炫酷的2022新年快乐html网页特效，霓虹的城市夜景和绚烂的烟花很是特别，该html页面还有交互效果，点击鼠标就会呈现烟花绽放的特效，唯美不过如此。图片可以换成自己喜欢的夜景或人物都可以。​

主要代码

图片选择引入：

html, body {
            margin: 0;
            padding: 0;
            overflow: hidden;
            background: #000;
            font-family: montserrat, sans-serif;
            background-image: url(img/pexels-photo-219692.jpeg);
            background-size: cover;
            background-position: center;
        }

css样式

html, body {
            margin: 0;
            padding: 0;
            overflow: hidden;
            background: #000;
            font-family: montserrat, sans-serif;
            background-image: url(img/pexels-photo-219692.jpeg);
            background-size: cover;
            background-position: center;
        }
 
        canvas {
            mix-blend-mode: lighten;
            cursor: pointer;
        }
 
        #hero {
            display: inline;
            position: absolute;
            top: 50%;
            left: 50%;
            transform: translate(-50%, -50%);
            mix-blend-mode: color-dodge;
        }
 
        #year {
            font-size: 30vw;
            color: #d0d0d0;
            font-weight: bold;
        }
 
        #timeleft {
            color: #fbfbfb;
            font-size: 2.5vw;
            text-align: center;
            font-family: lora, serif;
        }

javascirpt

const canvas = document.createelement('canvas'),
        context = canvas.getcontext('2d'),
        width = canvas.width = window.innerwidth,
        height = canvas.height = window.innerheight,
        halfpi = math.pi / 2,
        gravity = vector.create(0, 0.35),
        year = document.getelementbyid('year'),
        timeleft = document.getelementbyid('timeleft'),
        newyear = new date('01/01/2020');
 
    let objects = [],
        startfireworks = false,
        newyearalready = false;
 
    function rendertimeleft() {
        let date = new date();
 
        let delta = math.abs(newyear - date) / 1000;
 
        let hours = math.floor(delta / 3600) % 24;
        delta -= hours * 3600;
 
        let minutes = math.floor(delta / 60) % 60;
        delta -= minutes * 60;
 
        let seconds = math.floor(delta % 60) + 1;
 
        let string = '';
 
        let daysleft = math.floor((newyear - date) / (1000 * 60 * 60 * 24)),
            hoursleft = `${hours} ${hours > 1 ? 'hours' : 'hour'}`,
            minutesleft = `${minutes} ${minutes > 1 ? 'minutes' : 'minute'}`,
            secondsleft = `${seconds} ${seconds > 1 ? 'seconds' : 'second'}`;
 
        if (hours > 0) string = `${hoursleft} & ${minutesleft}`;else
        if (minutes > 0) string = `${minutesleft} & ${secondsleft}`;else
            string = `${secondsleft}`;
 
        if (daysleft > 0) string = daysleft + ' days, ' + string;
        string += ' until 2020';
 
        timeleft.innerhtml = string;
    }
 
    rendertimeleft();
 
    setinterval(function () {
        let date = new date();
        if (date >= newyear) {
            if (!newyearalready) {
                year.innerhtml = '2022';
                startfireworks = true;
                timeleft.innerhtml = 'happy new year!';
            }
 
            newyearalready = true;
        } else rendertimeleft();
    }, 500);
 
 
    document.body.appendchild(canvas);
 
    function random255() {
        return math.floor(math.random() * 100 + 155);
    }
 
    function randomcolor() {
        let r = random255(),
            g = random255(),
            b = random255();
        return `rgb(${r}, ${g}, ${b})`;
    }
 
    class physicsbody {
        constructor() {
            objects.push(this);
        }
        physicsupdate() {
            this.lastposition = this.position.duplicate();
            this.position.addto(this.velocity);
            this.velocity.addto(gravity);
        }
        deleteobject() {
            objects[objects.indexof(this)] = undefined;
        }}
 
 
    class firework extends physicsbody {
        constructor() {
            super();
            this.position = vector.create(math.random() * width, height);
 
            let velocity = vector.create(0, 0);
            velocity.setlength(math.random() * 10 + 15);
            velocity.setangle(math.pi * 1.35 + math.random() * math.pi * 0.30);
            this.velocity = velocity;
 
            this.trail = math.floor(math.random() * 4) != 1;
            this.trailcolor = this.trail ? randomcolor() : undefined;
            this.trailwidth = 2;
 
            this.timecreated = new date().gettime();
            this.timeexpired = this.timecreated + (math.random() * 5 + 7) * 100;
 
            this.blastparticlecount = math.floor(math.random() * 50) + 25;
            this.funky = math.floor(math.random() * 5) == 1;
 
            this.exposioncolor = randomcolor();
        }
 
        draw() {
            context.strokestyle = this.trailcolor;
            context.linewidth = this.trailwidth;
 
            let p = this.position,
                lp = this.lastposition;
 
            context.beginpath();
            context.moveto(lp.getx(), lp.gety());
            context.lineto(p.getx(), p.gety());
            context.stroke();
        }
 
        funkyfire() {
            var funky = this.funky;
            for (var i = 0; i < math.floor(math.random() * 10); i++) {
                new blastparticle({ firework: this, funky });
            }
        }
 
        explode() {
            var funky = this.funky;
            for (var i = 0; i < this.blastparticlecount; i++) {
                new blastparticle({ firework: this, funky });
            }
            this.deleteobject();
        }
 
        checkexpire() {
            let now = new date().gettime();
            if (now >= this.timeexpired) this.explode();
        }
 
        render() {
            if (this.trail) this.draw();
            if (this.funky) this.funkyfire();
            this.checkexpire();
        }}
 
 
    class blastparticle extends physicsbody {
        constructor({ firework, funky }) {
            super();
            this.position = firework.position.duplicate();
 
            let velocity = vector.create(0, 0);
            if (!this.funky) {
                velocity.setlength(math.random() * 6 + 2);
                velocity.setangle(math.random() * math.pi * 2);
            } else {
                velocity.setlength(math.random() * 3 + 1);
                velocity.setangle(firework.getangle + math.pi / 2 - math.pi * 0.25 + math.pi * .5);
            }
 
            this.velocity = velocity;
 
            this.color = firework.exposioncolor;
 
            this.particlesize = math.random() * 4;
 
            this.timecreated = new date().gettime();
            this.timeexpired = this.timecreated + (math.random() * 4 + 3.5) * 100;
        }
 
        draw() {
            context.strokestyle = this.color;
            context.linewidth = this.particlesize;
            let p = this.position,
                lp = this.lastposition;
 
            context.beginpath();
            context.moveto(lp.getx(), lp.gety());
            context.lineto(p.getx(), p.gety());
            context.stroke();
        }
 
        checkexpire() {
            let now = new date().gettime();
            if (now >= this.timeexpired) this.deleteobject();
        }
 
        render() {
            this.draw();
            this.checkexpire();
        }}
 
 
    document.body.addeventlistener('mousedown', function (e) {
        let color = randomcolor();
        for (var i = 0; i < math.floor(math.random() * 20) + 25; i++) {
            new blastparticle({
                firework: {
                    position: vector.create(e.pagex, e.pagey),
                    velocity: vector.create(0, 0),
                    exposioncolor: color },
 
                funky: false });
 
        }
    });
 
    setinterval(function () {
        if (!startfireworks) return;
        for (var i = 0; i < math.floor(math.random() * 4); i++) {
            new firework();
        }
    }, 500);
 
    function cleanupobjects() {
        objects = objects.filter(o => o != undefined);
    }
 
    function loop() {
        context.fillstyle = 'rgba(0,0,0,0.085)';
        context.fillrect(0, 0, width, height);
 
        let unusedobjectcount = 0;
        objects.map(o => {
            if (!o) {unusedobjectcount++;return;}
            o.physicsupdate();
            o.render();
        });
        if (unusedobjectcount > 100) cleanupobjects();
 
        requestanimationframe(loop);
    }
 
    loop();

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