function loading(element,lightColor,darkColor,speed,callback){
if(!element&&(!element.innerText||!element.textContent))return
element = typeof element==="string"?document.getElementById(element):element
lightColor = lightColor||"#fff",darkColor = darkColor||"#000",speed = speed||300

var arr_spanEles = new Array()

!function(arr_elementText){
element.innerText=element.textContent=""
for(var i=0;i<arr_elementText.length;i++){
var span = document.createElement("span")
element.innerText?span.innerText = arr_elementText[i]:span.textContent = arr_elementText[i]
element.appendChild(span)
arr_spanEles.push(span)
}
}((element.innerText||element.textContent).split(""))

var index = -1,length = arr_spanEles.length
var loadingTimer = setInterval(function(){
arr_spanEles[Math.max(index,0)].style.color = darkColor
if(index == length-1){
index = -1
callback&&callback()
}
++index
arr_spanEles[index].style.color = lightColor
},speed)
}