JavaScript渐变效果的实现

先来看一下效果演示：

#runs{width:300px; margin:10px auto;}
#runs li{width:80px; height:80px; background:#06c; list-style:none; float:left; margin:10px; display:inline; filter:alpha(opacity=30); opacity:0.3;}

window.onload = function(){
var runs = document.getElementById("runs");
var runs_li = runs.getElementsByTagName("li");
var i=0;
for(i=0; iobj.alpha){
speed = 5;
}else{
speed = -5;
}

if(obj.alpha == target){
clearInterval(obj.timer);
}else{
obj.alpha = obj.alpha + speed;
obj.style.filter = "alpha(opacity="+obj.alpha+")";
obj.style.opacity = obj.alpha/100;
}

},30)
}

简

明

现

代

魔

法

上面的元素，鼠标移上去透明度渐渐增加，鼠标移出，透明度渐渐减小。

关键代码：

var speed = 0;
if(target>obj.alpha){
	speed = 5;
}else{
	speed = -5;
}

根据目标值和当时值的对比，来决定是正向还是负向速度。

for(i=0; i < runs_li.length; i++){
	runs_li[i].timer = null;
	runs_li[i].alpha = 30;
	runs_li[i].onmouseover = function(){
		startrun(this,100);
	}
	runs_li[i].onmouseout = function(){
		startrun(this,30);
	}
}

给每一个元素加上各自的透明度值，各自的透明度变化分开。

全部代码：

<style>
#runs{width:300px; margin:10px auto;}
#runs li{width:80px; height:80px; background:#06c; list-style:none; float:left; margin:10px; display:inline; filter:alpha(opacity=30); opacity:0.3;}
</style>
<script>
window.onload = function(){
  var runs = document.getElementById("runs");
  var runs_li = runs.getElementsByTagName("li");
  var i=0; 
  for(i=0; i<runs_li.length; i++){
    runs_li[i].timer = null;
    runs_li[i].alpha = 30;
    runs_li[i].onmouseover = function(){
      startrun(this,100);
    }
    runs_li[i].onmouseout = function(){
      startrun(this,30);
    }
  }
}

function startrun(obj,target){
  clearInterval(obj.timer);
  obj.timer = setInterval(function(){
    var speed = 0;
    if(target>obj.alpha){
      speed = 5;
    }else{
      speed = -5;
    }
    
    if(obj.alpha == target){
      clearInterval(obj.timer);
    }else{
      obj.alpha = obj.alpha + speed;
      obj.style.filter = "alpha(opacity="+obj.alpha+")";
      obj.style.opacity = obj.alpha/100;
    }
  
  },30)
}

</script>

<ul id="runs">
  <li>简</li>
  <li>明</li>
  <li>现</li>
  <li>代</li>
  <li>魔</li>
  <li>法</li>
</ul>