每天一个JS 小demo之通过键盘方向键操作图片上下左右无缝切换。主要知识点：事件 - catEatBird_H5之家

<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Document</title>
<style type="text/css">
.wrap {
margin: 150px auto;
position: relative;
width: 400px;
height: 300px;
overflow: hidden;
border: 2px solid #000;
}
.wrap img {
position: absolute;
}
</style>
</head>
<body>
<div>
<img src="pic/1.jpg" />
<img src="pic/2.jpg" />
</div>
<script type="text/javascript" src="js/startmove.js"></script>
<script type="text/javascript">
(function(){
var data = ["pic/1.jpg","pic/2.jpg","pic/3.jpg","pic/4.jpg"];
var img = document.querySelectorAll('img');
var now = 0;
var next = 0;
var imgW = css(img[0],"width");
var imgH = css(img[0],"height");
var isMove = false;
document.addEventListener('keyup', function(e) {
if(isMove){
return;
}
switch(e.keyCode){
case 37:
//向左
toLeft();
break;
case 38:
//向上
toUp();
break;
case 39:
//向右
toRight();
break;
case 40:
//向下
toDown();
break;
}
});
function toLeft(){
next = (now + 1)%data.length;
init([0,0,0,imgW],{left:-imgW},{left:0});
}
function toUp(){
next = (now + 1)%data.length;
init([0,0,imgH,0],{top:-imgH},{top:0});
}
function toRight(){
next = (now - 1 + data.length)%data.length;
init([0,0,0,-imgW],{left:imgW},{left:0});
}
function toDown(){
next = (now - 1 + data.length)%data.length;
init([0,0,-imgH,0],{top:imgH},{top:0});
}
// styles = [0,0,0,0];
// target1 {}
//init 初始位置
function init(styles,target1,target2){
isMove = true;
img[0].src= data[now];
img[1].src= data[next];
css(img[0],"top",styles[0]);
css(img[0],"left",styles[1]);
css(img[1],"top",styles[2]);
css(img[1],"left",styles[3]);
now = next;
move(img[0],target1);
move(img[1],target2,function(){
isMove = false;
});
}
// 移动
function move(el,target,callBack){
startMove({
el:el,
target:target,
type: "easeOut",
time: 1000
});
}
})();
</script>
</body>
</html>

//动画形式公式
var Tween = {
linear: function (t, b, c, d){
return c*t/d + b;
},
easeIn: function(t, b, c, d){
return c*(t/=d)*t + b;
},
easeOut: function(t, b, c, d){
return -c *(t/=d)*(t-2) + b;
},
easeBoth: function(t, b, c, d){
if ((t/=d/2) < 1) {
return c/2*t*t + b;
}
return -c/2 * ((--t)*(t-2) - 1) + b;
},
easeInStrong: function(t, b, c, d){
return c*(t/=d)*t*t*t + b;
},
easeOutStrong: function(t, b, c, d){
return -c * ((t=t/d-1)*t*t*t - 1) + b;
},
easeBothStrong: function(t, b, c, d){
if ((t/=d/2) < 1) {
return c/2*t*t*t*t + b;
}
return -c/2 * ((t-=2)*t*t*t - 2) + b;
},
elasticIn: function(t, b, c, d, a, p){
if (t === 0) {
return b;
}
if ( (t /= d) == 1 ) {
return b+c;
}
if (!p) {
p=d*0.3;
}
if (!a || a < Math.abs(c)) {
a = c;
var s = p/4;
} else {
var s = p/(2*Math.PI) * Math.asin (c/a);
}
return -(a*Math.pow(2,10*(t-=1)) * Math.sin( (t*d-s)*(2*Math.PI)/p )) + b;
},
elasticOut: function(t, b, c, d, a, p){
if (t === 0) {
return b;
}
if ( (t /= d) == 1 ) {
return b+c;
}
if (!p) {
p=d*0.3;
}
if (!a || a < Math.abs(c)) {
a = c;
var s = p / 4;
} else {
var s = p/(2*Math.PI) * Math.asin (c/a);
}
return a*Math.pow(2,-10*t) * Math.sin( (t*d-s)*(2*Math.PI)/p ) + c + b;
},
elasticBoth: function(t, b, c, d, a, p){
if (t === 0) {
return b;
}
if ( (t /= d/2) == 2 ) {
return b+c;
}
if (!p) {
p = d*(0.3*1.5);
}
if ( !a || a < Math.abs(c) ) {
a = c;
var s = p/4;
}
else {
var s = p/(2*Math.PI) * Math.asin (c/a);
}
if (t < 1) {
return - 0.5*(a*Math.pow(2,10*(t-=1)) *
Math.sin( (t*d-s)*(2*Math.PI)/p )) + b;
}
return a*Math.pow(2,-10*(t-=1)) *
Math.sin( (t*d-s)*(2*Math.PI)/p )*0.5 + c + b;
},
backIn: function(t, b, c, d, s){
if (typeof s == 'undefined') {
s = 1.70158;
}
return c*(t/=d)*t*((s+1)*t - s) + b;
},
backOut: function(t, b, c, d, s){
if (typeof s == 'undefined') {
s = 2.70158; //回缩的距离
}
return c*((t=t/d-1)*t*((s+1)*t + s) + 1) + b;
},
backBoth: function(t, b, c, d, s){
if (typeof s == 'undefined') {
s = 1.70158;
}
if ((t /= d/2 ) < 1) {
return c/2*(t*t*(((s*=(1.525))+1)*t - s)) + b;
}
return c/2*((t-=2)*t*(((s*=(1.525))+1)*t + s) + 2) + b;
},
bounceIn: function(t, b, c, d){
return c - Tween['bounceOut'](d-t, 0, c, d) + b;
},
bounceOut: function(t, b, c, d){
if ((t/=d) < (1/2.75)) {
return c*(7.5625*t*t) + b;
} else if (t < (2/2.75)) {
return c*(7.5625*(t-=(1.5/2.75))*t + 0.75) + b;
} else if (t < (2.5/2.75)) {
return c*(7.5625*(t-=(2.25/2.75))*t + 0.9375) + b;
}
return c*(7.5625*(t-=(2.625/2.75))*t + 0.984375) + b;
},
bounceBoth: function(t, b, c, d){
if (t < d/2) {
return Tween['bounceIn'](t*2, 0, c, d) * 0.5 + b;
}
return Tween['bounceOut'](t*2-d, 0, c, d) * 0.5 + c*0.5 + b;
}
}
// 获取或者设置样式
function css(el,attr,val){
if(arguments.length == 2){
if(el.currentStyle){
val = el.currentStyle[attr];
} else {
val = getComputedStyle(el)[attr];
}
return parseFloat(val);
} else {
if(attr == "opacity"){
el.style.opacity = val;
el.style.filter = "alpha(opacity= "+val*100+")";
} else if(attr == "zIndex"){
el.style[attr] = Math.round(val);
}else {
el.style[attr] = val + "px";
}
}
}
//执行动画
function startMove(init){
clearInterval(init.el.timer);
var t = 0;
var b = {};
var c = {};
var d = init.time/20;
for( var s in init.target){
b[s] = css(init.el,s);
c[s] = init.target[s] - b[s];
}
init.el.timer = setInterval(function(){
t++;
if(t > d){
clearInterval(init.el.timer);
init.callBack&&init.callBack();
} else {
for(var s in init.target){
var val = Tween[init.type](t,b[s],c[s],d);
css(init.el,s,val);
}
}
},20);
}