原生JS实现文件上传按钮及图片缩略图预览

<html>
 <head>
 <meta charset="utf-8" />
 <title>uploalFileButton</title>
 <link rel="stylesheet" href="style.css" />
 </head>
 <body>
 <div class="file-container">
 <div class="file-box">
 <input type="file" class="file-btn" accept="image/png,image/jpeg,image/gif" id="file" />
 <text>选择文件</text>
 </div>
 <span id="showFileName"></span>
 <span id="fileerrorTip"></span>
 <div class="show_image">
 <img src="" id="file_img" />
 </div>
 </div>
 
 <script type="text/javascript" src="script.js"></script>
 </body>
</html>

(function(){
 var fileBtn = document.getElementById('file');
 var showName = document.getElementById('showFileName');
 var errorTip = document.getElementById('fileerrorTip');
 var fileImg = document.getElementById('file_img');

 fileBtn.onchange = function(){
 try{
 var fileName = this.files[0].name;
 // 限制图片上传类型
 if(fileName.indexOf("jpg") != -1 || fileName.indexOf("png") != -1) {
 errorTip.innerHTML = "";
 showName.innerHTML = fileName;
 //显示预览图片
 var file = this.files[0];
 var reader = new FileReader();
 reader.readAsDataURL(file);
 reader.onloadend = function(e) {
 fileImg.src = e.target.result;
 fileImg.style["display"] = "unset";
 };
 } else {
 showName.innerHTML = "";
 errorTip.innerHTML = "您未上传文件，或者您上传文件类型有误！";
 return false
 }
 }catch(e){}
 }
})()

.file-container{
 display: inline-block;
}

.file-box{
 display: inline-block;
 position: relative;
 padding:8px 25px;
 overflow: hidden;
 color:#fff;
 background-color: #4387CD;
 border-radius: 5px;
 cursor: pointer;
 vertical-align: bottom;
}

.file-btn{
 position: absolute;
 width: 100%;
 height: 100%;
 top: 0;
 left: 0;
 outline: none;
 filter:alpha(opacity=0);
 opacity: 0;
}

#showFileName, #fileerrorTip{
 vertical-align: bottom;
}

.show_image{
 width: 100px;
 padding: 5px;
 margin: 5px 0;
 border: 1px solid #ccc;
 border-radius: 5px;
}

.show_image img{
 display: none;
 width: 100px;
}