//file 为file传入的值(onchange="previewimg(this)")
function previewimg(file) { var maxwidth = 70; var maxheight = 80; if (file.files && file.files[0]) { var extension = "." + file.files[0].name.split('.')[1]; var result = $.inArray(extension, filetype); if (result == -1) { alert("只能是.gif, .png, .jpg, .jpeg, .bmp等格式的图片"); return; } //pre_img 为 预览 img标签的id var img = document.getElementById('pre_img'); 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]); } } function clacImgZoomParam(maxwidth, maxheight, width, height) { var param = { top: 0, left: 0, width, height: height }; if (width > maxwidth || height > maxheight) { param.width = maxwidth; param.height = maxheight; } return param; }