jQuery实现本地预览上传图片功能

本文实例介绍了基于JQUERY扩展，图片上传预览插件，目前兼容浏览器(IE 谷歌 火狐) 不支持safari，分享给大家供大家参考，具体内容如下

HTML代码：

<html>
<head>
<title>图片上传预览演示</title>
<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.7.1/jquery.min.js" type="text/javascript"></script>
<script src="16/uploadPreview.js" type="text/javascript"></script>
<script>
$(function () {
$("#up").uploadPreview({ Img: "ImgPr", Width: 120, Height: 120 });
});
</script>
</head>
<body>
<div style="width:500px;margin:0px auto;"><h2>图片上传预览演示</h2>
<a href="# target="_blank">原文</a>

<div><img id="ImgPr" width="120" height="120" /></div>
<input type="file" id="up" />
</div>

</body>
</html>

js代码：

*参数说明: Img:图片ID;Width:预览宽度;Height:预览高度;ImgType:支持文件类型;Callback:选择文件显示图片后回调方法;
*使用方法:
<div>
<img id="ImgPr" width="120" height="120" /></div>
<input type="file" id="up" />
把需要进行预览的IMG标签外 套一个DIV 然后给上传控件ID给予uploadPreview事件
$("#up").uploadPreview({ Img: "ImgPr", Width: 120, Height: 120, ImgType: ["gif", "jpeg", "jpg", "bmp", "png"], Callback: function () { }});
*/
jQuery.fn.extend({
uploadPreview: function (opts) {
var _self = this,
_this = $(this);
opts = jQuery.extend({
Img: "ImgPr",
Width: 100,
Height: 100,
ImgType: ["gif", "jpeg", "jpg", "bmp", "png"],
Callback: function () {}
}, opts || {});
_self.getObjectURL = function (file) {
var url = null;
if (window.createObjectURL != undefined) {
url = window.createObjectURL(file)
} else if (window.URL != undefined) {
url = window.URL.createObjectURL(file)
} else if (window.webkitURL != undefined) {
url = window.webkitURL.createObjectURL(file)
}
return url
};
_this.change(function () {
if (this.value) {
if (!RegExp("\.(" + opts.ImgType.join("|") + ")$", "i").test(this.value.toLowerCase())) {
alert("选择文件错误,图片类型必须是" + opts.ImgType.join("，") + "中的一种");
this.value = "";
return false
}
if ($.browser.msie) {
try {
$("#" + opts.Img).attr('src', _self.getObjectURL(this.files[0]))
} catch (e) {
var src = "";
var obj = $("#" + opts.Img);
var div = obj.parent("div")[0];
_self.select();
if (top != self) {
window.parent.document.body.focus()
} else {
_self.blur()
}
src = document.selection.createRange().text;
document.selection.empty();
obj.hide();
obj.parent("div").css({
'filter': 'progid:DXImageTransform.Microsoft.AlphaImageLoader(sizingMethod=scale)',
'width': opts.Width + 'px',
'height': opts.Height + 'px'
});
div.filters.item("DXImageTransform.Microsoft.AlphaImageLoader").src = src
}
} else {
$("#" + opts.Img).attr('src', _self.getObjectURL(this.files[0]))
}
opts.Callback()
}
})
}
});

直接上第二段代码，jquery js实现上传图片之前预览本地图片

<style type="text/css">
#preview_wrapper{
  display:inline-block;
  width:300px;
  height:300px;
  background-color:#CCC;
}
#preview_fake{
  filter:progid:DXImageTransform.Microsoft.AlphaImageLoader(sizingMethod=scale);
}
#preview_size_fake{
  filter:progid:DXImageTransform.Microsoft.AlphaImageLoader(sizingMethod=image);
  visibility:hidden;
}
#preview{
  width:300px;
  height:300px;
}
</style>

<script type="text/javascript">
function onUploadImgChange(sender){
  if( !sender.value.match( /.jpg|.gif|.png|.bmp/i ) ){
    alert('图片格式无效！');
    return false;
  }
  var objPreview = document.getElementByIdx_x('preview');
  var objPreviewFake = document.getElementByIdx_x('preview_fake');
  var objPreviewSizeFake = document.getElementByIdx_x('preview_size_fake');
  if( sender.files && sender.files[0] ){
    objPreview.style.display = 'block';
    objPreview.style.width = 'auto';
    objPreview.style.height = 'auto';  

    // Firefox 因安全性问题已无法直接通过 input[file].value 获取完整的文件路径
    objPreview.src = sender.files[0].getAsDataURL();
  }else if( objPreviewFake.filters ){
    // IE7,IE8 在设置本地图片地址为 img.src 时出现莫名其妙的后果
    //（相同环境有时能显示，有时不显示），因此只能用滤镜来解决  

    // IE7, IE8因安全性问题已无法直接通过 input[file].value 获取完整的文件路径
    sender.select();
    var imgSrc = document.selection.createRange().text;  

    objPreviewFake.filters.item(
      'DXImageTransform.Microsoft.AlphaImageLoader').src = imgSrc;
    objPreviewSizeFake.filters.item(
      'DXImageTransform.Microsoft.AlphaImageLoader').src = imgSrc;  

    autoSizePreview( objPreviewFake,
      objPreviewSizeFake.offsetWidth, objPreviewSizeFake.offsetHeight );
    objPreview.style.display = 'none';
  }
}  

function onPreviewLoad(sender){
  autoSizePreview( sender, sender.offsetWidth, sender.offsetHeight );
}  

function autoSizePreview( objPre, originalWidth, originalHeight ){
  var zoomParam = clacImgZoomParam( 300, 300, originalWidth, originalHeight );
  objPre.style.width = zoomParam.width + 'px';
  objPre.style.height = zoomParam.height + 'px';
  objPre.style.marginTop = zoomParam.top + 'px';
  objPre.style.marginLeft = zoomParam.left + 'px';
}  

function clacImgZoomParam( maxWidth, maxHeight, width, height ){
  var param = { width:width, height:height, top:0, left:0 };  

  if( width>maxWidth || height>maxHeight ){
    rateWidth = width / maxWidth;
    rateHeight = height / maxHeight;  

    if( rateWidth > rateHeight ){
      param.width = maxWidth;
      param.height = height / rateWidth;
    }else{
      param.width = width / rateHeight;
      param.height = maxHeight;
    }
  }  

  param.left = (maxWidth - param.width) / 2;
  param.top = (maxHeight - param.height) / 2;  

  return param;
}
</script>

<input name="localfile" type="file" id="localfile" size="28" onchange="onUploadImgChange(this)"/>

<!--以下是预览图片用的-->
<div id="preview_wrapper">
<div id="preview_fake">
<img id="preview" src="" onload="onPreviewLoad(this)"/>
</div>
</div>
<br/>
<img id="preview_size_fake" />

以上就是本文的全部内容，希望对大家的学习有所帮助。