我正在尝试将本地图像加载为缩略图，如此处所述。我的代码如下。
这适用于小图像。但是，当您尝试加载更大的图像（例如 4mb）时，会有很大的延迟。有没有办法优化这个？
谢谢
html
<input type="file" id="files" name="files[]" multiple />
<output id="list"></output>
Javascript
<script>
function handleFileSelect(evt) {
var files = evt.target.files; // FileList object
// Loop through the FileList and render image files as thumbnails.
for (var i = 0, f; f = files[i]; i++) {
// Only process image files.
if (!f.type.match('image.*')) {
continue;
}
var reader = new FileReader();
// Closure to capture the file information.
reader.onload = (function(theFile) {
return function(e) {
// Render thumbnail.
var span = document.createElement('span');
span.innerHTML = ['<img class="thumb" src="', e.target.result,
'" title="', escape(theFile.name), '"/>'].join('');
document.getElementById('list').insertBefore(span, null);
};
})(f);
// Read in the image file as a data URL.
reader.readAsDataURL(f);
}
}
document.getElementById('files').addEventListener('change', handleFileSelect, false);
</script>