多屏判断css改写

 function replaceBodyClass(){
     for(var i in map){
        if(map[i](width)){
           document.body.className = document.body.className.replace(/screen-\w+/, "screen-"+i)
           break
        }
     }
 }

 map["1280"] = function(width){
    return width <= 1300
 }

 map["x1"] = function(width){
    return width > = 1580
 }

 map["1"] = function(width){
    return  width > = 1400 && width < 1580
 }