js修改input file标签样式的方法

<form action="" method="" enctype=&#39;multipart/form-data&#39;>
   <label for=&#39;my_file&#39; class=&#39;inputlabelBox&#39;>
           <p class="inputBox">点击上传文件</p>
    </label>
    <input type="file" name="myfile" id=&#39;my_file&#39; style="display:none;" />
</form>
<img src="" id="img" width="300" />

var inputlabelBox = document.querySelector('.inputlabelBox');
var my_file = document.querySelector('#my_file');
var img = document.querySelector('#img'); 
my_file.onchange = function()
{       
         var file = this.files[0];
         var reader = new FileReader();
         reader.readAsDataURL(file);
         reader.onload = function()
         {
                img.src = this.result;
         }
}