上传图片并实现本地预览

该方法兼容IE浏览器。

<img id="preview1" src="" alt="" />
<input type = "file" onchange = "previewImage(this,1)" />

function previewImage(file, imgNum) {
        var MAXWIDTH = 188;
        var MAXHEIGHT = 80;
        var div = document.getElementById('preview' + imgNum);
        if (file.files && file.files[0]) {
            div.innerHTML = '<img id=imghead' + imgNum + '>';
            var img = document.getElementById('imghead' + imgNum + '');
            $(".icon_guanbi").click(function () {
                div.innerHTML = '';
            })
            img.onload = function () {
                var rect = clacImgZoomParam(MAXWIDTH, MAXHEIGHT, img.offsetWidth, img.offsetHeight);
                img.width = rect.width;
                img.height = rect.height;
//         img.style.marginLeft = rect.left+'px';
                img.style.marginTop = rect.top + 'px';
            }
            var reader = new FileReader();
            reader.onload = function (evt) {
                img.src = evt.target.result;
            }
            reader.readAsDataURL(file.files[0]);
        }
        else //
        {
            var sFilter = 'filter:progid:DXImageTransform.Microsoft.AlphaImageLoader(sizingMethod=scale,src="';
            file.select();
            var src = document.selection.createRange().text;
            div.innerHTML = '<img id=imghead' + imgNum + '>';
            var img = document.getElementById('imghead2');
            img.filters.item('DXImageTransform.Microsoft.AlphaImageLoader').src = src;
            var rect = clacImgZoomParam(MAXWIDTH, MAXHEIGHT, img.offsetWidth, img.offsetHeight);
            status = ('rect:' + rect.top + ',' + rect.left + ',' + rect.width + ',' + rect.height);
            div.innerHTML = "<div id=divhead" + imgNum + " style='width:" + rect.width + "px;height:" + rect.height + "px;margin-top:" + rect.top + "px;" + sFilter + src + "\"'></div>";
        }
    }
    function clacImgZoomParam(maxWidth, maxHeight, width, height) {
        var param = {top: 0, left: 0, width: width, height: height};
        if (width > maxWidth || height > maxHeight) {
            rateWidth = width / maxWidth;
            rateHeight = height / maxHeight;

            if (rateWidth > rateHeight) {
                param.width = maxWidth;
                param.height = Math.round(height / rateWidth);
            } else {
                param.width = Math.round(width / rateHeight);
                param.height = maxHeight;
            }
        }
        param.left = Math.round((maxWidth - param.width) / 2);
        param.top = Math.round((maxHeight - param.height) / 2);
        return param;
    }

参数说明：

previewImage(file,imgNum) file:input; imgNum:当前input对应预览的img的id编号

clacImgZoomParam(maxWidth, maxHeight, width, height)  maxWidth/maxHeight：图片父级宽高度  width/height：图片宽高度