点击图片来回切换图片--2张来回切换

<img src="img/1.jpg" alt="" id="img1">

window.onload = function(){
var img1 = document.getElementById('img1');
var onOff = true;//创造一个开关,布尔值，true为1，false为0

img1.onclick = function(){
if(onOff){//如果是真
img1.src = 'img/2.jpg';//图片路径切换为图片2
onOff = false;//并且开关设为假
}else{//如果是假
img1.src = 'img/1.jpg';//图片路径切换为图片1
onOff = true;//并且开关设为真
}
}
}