How to enlarge layui pictures

<div id="slideys" class="demo-slider"></div>

var ysw = 0;   //记录图片原始宽度
var ysh = 0;   //记录图片原始高度
layui.use('slider', function(){     
var $ = layui.$      
,slider = layui.slider;     
slider.render({            
elem: '#slideys'             
,value: 0 //初始值             
,theme: '#1E9FFF'            
,step: 1 //步长            
,min: -10 //最小值            
,max: 10 //最大值            
,showstep: true //开启间隔点            
,change: function(value){                
if(ysw ==0 || ysh == 0){                    
return;                
}                
var pjw = ysw/20;                
var pjh = ysh/20;                
var img =  $("#dximg");  //图片ID                
if(img!=null){                    
var w = Math.round(ysw+(pjw*value));                    
var h = Math.round(ysh+(pjh*value));                    
$(img).css("width", w );                      
$(img).css("height", h );                 
}              
}          
});    
});