教你3分钟利用原生js实现有进度监听的文件上传预览组件

<div id="test"></div><script src="./js/xjFile.js"></script><script> new xjFile({  el: '#test', // 不填则直接默认挂在body上  accept: 'image/png', // 可选  clsName: 'xj-wrap', // 可选  beforeUpload: function(e) { console.log(e) }, // 可选  onProgress: function(e) { console.log(e) }, // 可选  onLoad: function(e) { console.log(e) }, // 可选  onError: function(e) { console.error('文件读取错误', e) } // 可选 });</script>

.xj-wrap {   position: relative;   display: inline-block;   border: 1px dashed #888;   width: 200px;   height: 200px;   border-radius: 6px;   overflow: hidden;  }  .xj-wrap::before {   content: '+';   font-size: 36px;   position: absolute;   transform: translate(-50%, -50%);   left: 50%;   top: 50%;   color: #ccc;  }  .xj-wrap .xj-pre-img {   width: 100%;   height: 100%;   background-repeat: no-repeat;   background-position: center center;   background-size: 100%;  }  .xj-file {   position: absolute;   left: 0;   right: 0;   bottom: 0;   top: 0;   opacity: 0;   cursor: pointer;  }

(function(win, doc){ function xjFile(opt) {  var defaultOption = {   el: doc.body,   accept: '*', // 格式按照'image/jpg,image/gif'传   clsName: 'xj-wrap',   beforeUpload: function(e) { console.log(e) },   onProgress: function(e) { console.log(e) },   onLoad: function(e) { console.log(e) },   onError: function(e) { console.error('文件读取错误', e) }  };  // 获取dom  if(opt.el) {   opt.el = typeof opt.el === 'object' ? opt.el : document.querySelector(opt.el);  }  this.opt = minix(defaultOption, opt);  this.value = '';  this.init(); } xjFile.prototype.init = function() {  this.render();  this.watch(); } xjFile.prototype.render = function() {  var fragment = document.createDocumentFragment(),   file = document.createElement('input'),   imgBox = document.createElement('div');  file.type = 'file';  file.accept = this.opt.accept || '*';  file.className = 'xj-file';  imgBox.className = 'xj-pre-img';  // 插入fragment  fragment.appendChild(file);  fragment.appendChild(imgBox);  // 给包裹组件设置class  this.opt.el.className = this.opt.clsName;  this.opt.el.appendChild(fragment); } xjFile.prototype.watch = function() {  var ipt = this.opt.el.querySelector('.xj-file');  var _this = this;  ipt.addEventListener('change', (e) => {   var file = ipt.files[0];   // 给组件赋值   _this.value = file;   var fileReader = new FileReader();   // 读取文件开始时触发   fileReader.onloadstart = function(e) {    if(_this.opt.accept !== '*' && _this.opt.accept.indexOf(file.type.toLowerCase()) === -1) {     fileReader.abort();     _this.opt.beforeUpload(file, e);     console.error('文件格式有误', file.type.toLowerCase());    }   }   // 读取完成触发的事件   fileReader.onload = (e) => {    var imgBox = this.opt.el.querySelector('.xj-pre-img');    if(isImage(file.type)) {     imgBox.innerHTML = '';     imgBox.style.backgroundImage = 'url(' + fileReader.result + ')';    } else {     imgBox.innerHTML = fileReader.result;    }        imgBox.title = file.name;    this.opt.onLoad(e);   }   // 文件读取出错事件   fileReader.onerror = (e) => {    this.opt.onError(e);   }   // 文件读取进度事件   fileReader.onprogress = (e) => {    this.opt.onProgress(e);   }   isImage(file.type) ? fileReader.readAsDataURL(file) : fileReader.readAsText(file);     }, false); } // 清除ipt和组件的值，支持链式调用 xjFile.prototype.clearFile = function() {  this.opt.el.querySelector('.xj-file').value = '';  this.value = '';  return this } // 简单对象混合 function minix(source, target) {  for(var key in target) {   source[key] = target[key];  }  return source } // 检测图片类型 function isImage(type) {  var reg = /(image//jpeg|image//jpg|image//gif|image//png)/gi;  return reg.test(type) } // 将方法挂载到window上 win.xjFile = xjFile;})(window, document);

class XjFile { constructor(opt) { } init() { } watch() { } render() { } clearFile() { } minix(source, target) {   } isImage(type) {   }}