input type=file 上傳圖片前預覽 親測支援 ie8 chrome ff android及ios瀏覽器（將網上的版本整合一下）
阿新 • • 發佈：2019-02-01
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <title>Firefox3,IE6,IE7,IE8上傳圖片預覽</title> <style type="text/css">#preview_wrapper{ display:inline-block; width:100px; height:100px; background-color:#CCC; } #preview_fake{ /* 該物件使用者在IE下顯示預覽圖片 */ filter:progid:DXImageTransform.Microsoft.AlphaImageLoader(sizingMethod=scale); } #preview_size_fake{ /* 該物件只用來在IE下獲得圖片的原始尺寸，無其它用途 */ filter:progid:DXImageTransform.Microsoft.AlphaImageLoader(sizingMethod=image); visibility:hidden; } #preview{ /* 該物件使用者在FF下顯示預覽圖片 */ width:100px; height:100px; }</style> <script type="text/javascript">function onUploadImgChange(sender) { if (!sender.value.match(/.jpg|.jpeg|.png/i)) { alert('圖片格式無效！'); return false; } var objPreview = document.getElementById('preview'); var objPreviewFake = document.getElementById('preview_fake'); var objPreviewSizeFake = document.getElementById('preview_size_fake'); if (sender.files && sender.files[0]) { objPreview.style.display = 'block'; objPreview.style.width = 'auto'; objPreview.style.height = 'auto'; // Firefox 因安全性問題已無法直接通過 input[file].value 獲取完整的檔案路徑 if (window.createObjectURL != undefined) { // basic objPreview.src = window.createObjectURL(sender.files[0]); } else if (window.URL != undefined) { // mozilla(firefox) objPreview.src = window.URL.createObjectURL(sender.files[0]); } else if (window.webkitURL != undefined) { // webkit or chrome objPreview.src = window.webkitURL.createObjectURL(sender.files[0]); } } else if (objPreviewFake.filters) { // IE7,IE8 在設定本地圖片地址為 img.src 時出現莫名其妙的後果 //（相同環境有時能顯示，有時不顯示），因此只能用濾鏡來解決 // IE7, IE8因安全性問題已無法直接通過 input[file].value 獲取完整的檔案路徑 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(100, 100, 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> </head> <body> <div id="preview_wrapper"> <div id="preview_fake"> <img id="preview" onload="onPreviewLoad(this)" /></div> </div> <br/> <input id="upload_img" type="file" onchange="onUploadImgChange(this)" /> <br/> <img id="preview_size_fake" /> </body> </html>