发布于 2017-01-19 11:34:10 | 113 次阅读 | 评论: 0 | 来源: 网友投递

这里有新鲜出炉的Javascript教程，程序狗速度看过来！

JavaScript客户端脚本语言

Javascript 是一种由Netscape的LiveScript发展而来的原型化继承的基于对象的动态类型的区分大小写的客户端脚本语言，主要目的是为了解决服务器端语言，比如Perl，遗留的速度问题，为客户提供更流畅的浏览效果。

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本篇文章主要是对js本地预览的简单实现方法进行了介绍，需要的朋友可以过来参考下，希望对大家有所帮助

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var ImagePreview = function(file, img, options) {

 this.file = $(file);//文件对象
 this.img = $(img);//预览图片对象

 this._preload = null;//预载图片对象
 this._data = "";//图像数据
 this._upload = null;//remote模式使用的上传文件对象

 var opt = this._setOptions(options);

 this.action = opt.action;
 this.timeout = opt.timeout;
 this.ratio = opt.ratio;
 this.maxWidth = opt.maxWidth;
 this.maxHeight = opt.maxHeight;

 this.onCheck = opt.onCheck;
 this.onShow = opt.onShow;
 this.onErr = opt.onErr;

 //设置数据获取程序
 this._getData = this._getDataFun(opt.mode);
 //设置预览显示程序
 this._show = opt.mode !== "filter" ? this._simpleShow : this._filterShow;
};
//根据浏览器获取模式
ImagePreview.MODE = $B.ie7 || $B.ie8 ? "filter" :
 $B.firefox ? "domfile" :
 $B.opera || $B.chrome || $B.safari ? "remote" : "simple";
//透明图片
ImagePreview.TRANSPARENT = $B.ie7 || $B.ie6 ?
 "mhtml:" + document.scripts[document.scripts.length - 1].getAttribute("src", 4) + "!blankImage" :
 "data:image/gif;base64,R0lGODlhAQABAIAAAP///wAAACH5BAEAAAAALAAAAAABAAEAAAICRAEAOw==";

ImagePreview.prototype = {
  //设置默认属性
  _setOptions: function(options) {
    this.options = {//默认值
  mode:  ImagePreview.MODE,//预览模式
  ratio:  0,//自定义比例
  maxWidth: 0,//缩略图宽度
  maxHeight: 0,//缩略图高度
  onCheck: function(){},//预览检测时执行
  onShow:  function(){},//预览图片时执行
  onErr:  function(){},//预览错误时执行
  //以下在remote模式时有效
  action:  undefined,//设置action
  timeout: 0//设置超时(0为不设置)
    };
    return $.extend(this.options, options || {});
  },
  //开始预览
  preview: function() {
 if ( this.file && false !== this.onCheck() ) {
  this._preview( this._getData() );
 }
  },

  //根据mode返回数据获取程序
  _getDataFun: function(mode) {
 switch (mode) {
  case "filter" :
   return this._filterData;
  case "domfile" :
   return this._domfileData;
  case "remote" :
   return this._remoteData;
  case "simple" :
  default :
   return this._simpleData;
 }
  },
  //滤镜数据获取程序
  _filterData: function() {
 this.file.select();
 try{
  return document.selection.createRange().text;
 } finally { document.selection.empty(); }
  },
  //domfile数据获取程序
  _domfileData: function() {
 return this.file.files[0].getAsDataURL();
  },
  //远程数据获取程序
  _remoteData: function() {
 this._setUpload();
 this._upload && this._upload.upload();
  },
  //一般数据获取程序
  _simpleData: function() {
 return this.file.value;
  },

  //设置remote模式的上传文件对象
  _setUpload: function() {
 if ( !this._upload && this.action !== undefined && typeof QuickUpload === "function" ) {
  var oThis = this;
  this._upload = new QuickUpload(this.file, {
   onReady: function(){
    this.action = oThis.action; this.timeout = oThis.timeout;
    var parameter = this.parameter;
    parameter.ratio = oThis.ratio;
    parameter.width = oThis.maxWidth;
    parameter.height = oThis.maxHeight;
   },
   onFinish: function(iframe){
    try{
     oThis._preview( iframe.contentWindow.document.body.innerHTML );
    }catch(e){ oThis._error("remote error"); }
   },
   onTimeout: function(){ oThis._error("timeout error"); }
  });
 }
  },

  //预览程序
  _preview: function(data) {
 //空值或相同的值不执行显示
 if ( !!data && data !== this._data ) {
  this._data = data; this._show();
 }
  },

  //设置一般预载图片对象
  _simplePreload: function() {
 if ( !this._preload ) {
  var preload = this._preload = new Image(), oThis = this,
   onload = function(){ oThis._imgShow( oThis._data, this.width, this.height ); };
  this._onload = function(){ this.onload = null; onload.call(this); }
  preload.onload = $B.ie ? this._onload : onload;
  preload.onerror = function(){ oThis._error(); };
 } else if ( $B.ie ) {
  this._preload.onload = this._onload;
 }
  },
  //一般显示
  _simpleShow: function() {
 this._simplePreload();
 this._preload.src = this._data;
  },

  //设置滤镜预载图片对象
  _filterPreload: function() {
 if ( !this._preload ) {
  var preload = this._preload = document.createElement("div");
  //隐藏并设置滤镜
  $D.setStyle( preload, {
   width: "1px", height: "1px",
   visibility: "hidden", position: "absolute", left: "-9999px", top: "-9999px",
   filter: "progid:DXImageTransform.Microsoft.AlphaImageLoader(sizingMethod='image')"
  });
  //插入body
  var body = document.body; body.insertBefore( preload, body.childNodes[0] );
 }
  },
  //滤镜显示
  _filterShow: function() {
 this._filterPreload();
 var preload = this._preload,
  data = this._data.replace(/[)'"%]/g, function(s){ return escape(escape(s)); });
 try{
  preload.filters.item("DXImageTransform.Microsoft.AlphaImageLoader").src = data;
 }catch(e){ this._error("filter error"); return; }
 //设置滤镜并显示
 this.img.style.filter = "progid:DXImageTransform.Microsoft.AlphaImageLoader(sizingMethod='scale',src=\"" + data + "\")";
 this._imgShow( ImagePreview.TRANSPARENT, preload.offsetWidth, preload.offsetHeight );
  },

  //显示预览
  _imgShow: function(src, width, height) {
 var img = this.img, style = img.style,
  ratio = Math.max( 0, this.ratio ) || Math.min( 1,
    Math.max( 0, this.maxWidth ) / width  || 1,
    Math.max( 0, this.maxHeight ) / height || 1
   );
 //设置预览尺寸
 style.width = Math.round( width * ratio ) + "px";
 style.height = Math.round( height * ratio ) + "px";
 //设置src
 img.src = src;
 this.onShow();
  },

  //销毁程序
  dispose: function() {
 //销毁上传文件对象
 if ( this._upload ) {
  this._upload.dispose(); this._upload = null;
 }
 //销毁预载图片对象
 if ( this._preload ) {
  var preload = this._preload, parent = preload.parentNode;
  this._preload = preload.onload = preload.onerror = null;
  parent && parent.removeChild(preload);
 }
 //销毁相关对象
 this.file = this.img = null;
  },
  //出错
  _error: function(err) {
 this.onErr(err);
  }
}

<input id="idFile" type="file" name="pic" /><img id="idImg" alt="" src="http://www.phperz.com/" />
<script>
var ip = new ImagePreview( $$("idFile"), $$("idImg"), {
 maxWidth: 200, maxHeight: 2000, action: "ImagePreview.ashx"
});
ip.img.src = ImagePreview.TRANSPARENT;
ip.file.onchange = function(){ ip.preview(); };
</script>