如何讓input（type="file"）選中的圖片顯示在指定盒子里

<input type="file" id="fileElem" multiple="" accept="image/*" onchange="handleFiles(this.files)">
<div id="filegroup"></div>

function handleFiles(files){  
 var image-group= document.getElementById("filegroup");
      for (var i = 0; i < files.length; i++) { 
            var img_box = document.createElement("div");
            img_box.setAttribute("class","file-content");
            var img = document.createElement("img");
            img.src = window.URL.createObjectURL(files[i]);
            img.height = 100;
            img.onload = function() {
                window.URL.revokeObjectURL(this.src);
            }
            img_box.appendChild(img);
            image-group.appendChild(img_box)
        }
}