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http://stackoverflow.com/questions/14069421/show-an-image-preview-before-upload
1 <input type="file" id="files" /> 2 <img id="image" /> 3 4 5 <script type="text/javascript"> 6 document.getElementById("files").onchange = function () { 7 var reader = new FileReader(); 8 9 reader.onload = function (e) { 10 // get loaded data and render thumbnail. 11 document.getElementById("image").src = e.target.result; 12 }; 13 14 // read the image file as a data URL. 15 reader.readAsDataURL(this.files[0]); 16 }; 17 </script>
https://developer.mozilla.org/en-US/docs/Web/API/FileReader/readAsDataURL
<!doctype html> <html lang="en"> <head> <meta charset="UTF-8"> <meta name="Generator" content="EditPlus?"> <meta name="Author" content=""> <meta name="Keywords" content=""> <meta name="Description" content=""> <title>Document</title> </head> <body> <input id="browse" type="file" onchange="previewFiles()" multiple> <div id="preview"></div> </body> </html> <script type="text/javascript"> <!-- function previewFiles() { var preview = document.querySelector(‘#preview‘); var files = document.querySelector(‘input[type=file]‘).files; function readAndPreview(file) { // Make sure `file.name` matches our extensions criteria if ( /\.(jpe?g|png|gif)$/i.test(file.name) ) { var reader = new FileReader(); reader.addEventListener("load", function () { var image = new Image(); image.height = 100; image.title = file.name; image.src = this.result; preview.appendChild( image ); }, false); reader.readAsDataURL(file); } } if (files) { [].forEach.call(files, readAndPreview); } } //--> </script>
原文：http://www.cnblogs.com/yuanjiangw/p/6371282.html