今天要写个脚本能够对上传文件进行分析, 需要HTML客户端使用JS分析文件.
About File API
HTML5为我们提供了一种与本地文件系统交互的标准方式:File API。该规范主要定义了以下数据结构:
- File: 文件对象,包含有文件名,文件大小,mimetype类型和对文件句柄引用等.
- FileList: 一个文件对象的数组.
- Blob: 操作分割文件到字节
To check your browser whether support HTML5 File-API
// Check for the various File API support.
function isSupportFileApi() {
if(window.File && window.FileList && window.FileReader && window.Blob) {
alert('The File APIs are supported in this browser!');//return true;
} else{
alert('The File APIs are not fully supported in this browser.');//return false;
}}
//A button to call this function
Use File Handle
Use Form: input type=file
- 可以使用新multiple属性来进行多选, 此时files需要用数组.
- output标签也是新对象,用来定义不同类型的输出,例如脚本的输出.
<input type="file" id="files" name="files[]" multiple />
<output id="list"></output>
<script>
function handleFileSelect(evt) {
var files = evt.target.files; // FileList object
// files is a FileList of File objects. List some properties.
var output = [];
for (var i = 0, f; f = files[i]; i++) {
output.push('<li><strong>', escape(f.name), '</strong> (', f.type || 'n/a', ') - ',
f.size, ' bytes, last modified: ',
f.lastModifiedDate ? f.lastModifiedDate.toLocaleDateString() : 'n/a',
'</li>');
}
document.getElementById('list').innerHTML = '<ul>' + output.join('') + '</ul>';
}
document.getElementById('files').addEventListener('change', handleFileSelect, false);
</script>
Use drag method
拖拽通过一个叫dataTransfer
的接口来获得拖拽的文件列表,更多关于dataTransfer。拖拽同样支持多选,用户可以拖拽多个文件。
<div id="drop_zone">Drop files here</div>
<output id="list2"></output>
<script>
function handleFileSelect2(evt) {
evt.stopPropagation();
evt.preventDefault();
var files = evt.dataTransfer.files; // FileList object.
// files is a FileList of File objects. List some properties.
var output = [];
for (var i = 0, f; f = files[i]; i++) {
output.push('<li><strong>', escape(f.name), '</strong> (', f.type || 'n/a', ') - ',
f.size, ' bytes, last modified: ',
f.lastModifiedDate ? f.lastModifiedDate.toLocaleDateString() : 'n/a',
'</li>');
}
document.getElementById('list2').innerHTML = '<ul>' + output.join('') + '</ul>';
}
function handleDragOver(evt) {
evt.stopPropagation();
evt.preventDefault();
evt.dataTransfer.dropEffect = 'copy'; // Explicitly show this is a copy.
}
// Setup the dnd listeners.
var dropZone = document.getElementById('drop_zone');
dropZone.addEventListener('dragover', handleDragOver, false);
dropZone.addEventListener('drop', handleFileSelect2, false);
</script>
Drop files here
Read the file
FileReader 包括四个异步读取文件的选项:
- FileReader.readAsBinaryString(Blob/File) - result 属性将包含二进制字符串形式的 file/blob 数据。每个字节均由一个 [0..255] 范围内的整数表示。
- FileReader.readAsText(Blob/File, opt_encoding) - result属性将包含文本字符串形式的 file/blob 数据。该字符串在默认情况下采用“UTF-8”编码。使用可选编码参数可指定其他格式。
- FileReader.readAsDataURL(Blob/File) - result 属性将包含编码为数据网址的 file/blob 数据。
- FileReader.readAsArrayBuffer(Blob/File) - result属性将包含 ArrayBuffer 对象形式的 file/blob 数据。
当您获取了 File 引用后,实例化 FileReader 对象,以便将其内容读取到内存中。加载结束后,将触发读取程序的 onload 事件,而其 result 属性可用于访问文件数据。
对您的 FileReader 对象调用其中某一种读取方法后,可使用 onloadstart、onprogress、onload、onabort、onerror 和 onloadend 跟踪其进度。
选择图片文件并预览
使用reader.readAsDataURL()
进行文件调用.
<style>
.thumb {
height: 75px;
border: 1px solid #000;
margin: 10px 5px 0 0;
}
</style>
<input type="file" id="files3" name="files[]" multiple />
<output id="list3"></output>
<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('list3').insertBefore(span, null);
};
})(f);
// Read in the image file as a data URL.
reader.readAsDataURL(f);
}
}
document.getElementById('files3').addEventListener('change', handleFileSelect, false);
</script>
选择Text型文件并查看
使用reader.readAsText()
进行文件调用.
<input type="file" id="files4" name="files[]" multiple />
<output id="list4"></output>
<script>
function handleFileTextSelect(evt) {
var files = evt.target.files;
for (var i = 0, f; f = files[i]; i++) {
var reader = new FileReader();
reader.onload = (function(theFile) {
return function(e) {
var span = document.createElement('span');
span.innerHTML = [e.target.result].join('');
document.getElementById('list4').insertBefore(span, null);
}
;}
)(f);
// Read in the file context.
reader.readAsText(f);}
}
document.getElementById('files4').addEventListener('change', handleFileTextSelect, false);
</script>
分割文件
该示例使用 onloadend 并检查 evt.target.readyState,而不是使用 onload 事件。
<style>
#byte_content {
margin: 5px 0;
max-height: 100px;
overflow-y: auto;
overflow-x: hidden;
}
#byte_range { margin-top: 5px; }
</style>
<input type="file" id="files5" name="file" /> Read bytes:
<span class="readBytesButtons">
<button data-startbyte="0" data-endbyte="4">1-5</button>
<button data-startbyte="5" data-endbyte="14">6-15</button>
<button data-startbyte="6" data-endbyte="7">7-8</button>
<button>entire file</button>
</span>
<div id="byte_range"></div>
<div id="byte_content"></div>
<script>
function readBlob(opt_startByte, opt_stopByte) {
var files = document.getElementById('files5').files;
if (!files.length) {
alert('Please select a file!');
return;
}
var file = files[0];
var start = parseInt(opt_startByte) || 0;
var stop = parseInt(opt_stopByte) || file.size - 1;
var reader = new FileReader();
// If we use onloadend, we need to check the readyState.
reader.onloadend = function(evt) {
if (evt.target.readyState == FileReader.DONE) { // DONE == 2
document.getElementById('byte_content').textContent = evt.target.result;
document.getElementById('byte_range').textContent =
['Read bytes: ', start + 1, ' - ', stop + 1,
' of ', file.size, ' byte file'].join('');
}
};
//The following sentence help to make it work
var blob = file.slice(start, stop + 1);
if (file.webkitSlice) {
var blob = file.webkitSlice(start, stop + 1);
} else if (file.mozSlice) {
var blob = file.mozSlice(start, stop + 1);
}
reader.readAsBinaryString(blob);
}
document.querySelector('.readBytesButtons').addEventListener('click', function(evt) {
if (evt.target.tagName.toLowerCase() == 'button') {
var startByte = evt.target.getAttribute('data-startbyte');
var endByte = evt.target.getAttribute('data-endbyte');
readBlob(startByte, endByte);
}
}, false);
</script>
Read bytes:
监控读取进度
在使用异步事件处理时还能顺便获得一项优势,那就是能够监控文件的读取进度;这对于读取大文件、查找错误和预测读取完成时间非常实用。onloadstart
和 onprogress
事件可用于监控读取进度。以下示例演示了如何通过显示进度条来监控读取状态。要查看进度指示器的实际效果,请尝试读取大文件或远程驱动器中的文件。
<style>
#progress_bar {
margin: 10px 0;
padding: 3px;
border: 1px solid #000;
font-size: 14px;
clear: both;
opacity: 0;
-moz-transition: opacity 1s linear;
-o-transition: opacity 1s linear;
-webkit-transition: opacity 1s linear;
}
#progress_bar.loading {
opacity: 1.0;
}
#progress_bar .percent {
background-color: #99ccff;
height: auto;
width: 0;
}
</style>
<input type="file" id="files6" name="file" />
<button onclick="abortRead();">Cancel read</button>
<div id="progress_bar"><div class="percent">0%</div></div>
<script>
var reader_;
var progress = document.querySelector('.percent');
function abortRead() {
reader_.abort();
}
function errorHandler(evt) {
switch(evt.target.error.code) {
case evt.target.error.NOT_FOUND_ERR:
alert('File Not Found!');
break;
case evt.target.error.NOT_READABLE_ERR:
alert('File is not readable');
break;
case evt.target.error.ABORT_ERR:
break; // noop
default:
alert('An error occurred reading this file.');
};
}
function updateProgress(evt) {
// evt is an ProgressEvent.
if (evt.lengthComputable) {
var percentLoaded = Math.round((evt.loaded / evt.total) * 100);
// Increase the progress bar length.
if (percentLoaded < 100) {
progress.style.width = percentLoaded + '%';
progress.textContent = percentLoaded + '%';
}
}
}
function handleFileSelect(evt) {
// Reset progress indicator on new file selection.
progress.style.width = '0%';
progress.textContent = '0%';
reader_ = new FileReader();
reader_.onerror = errorHandler;
reader_.onprogress = updateProgress;
reader_.onabort = function(e) {
alert('File read cancelled');
};
reader_.onloadstart = function(e) {
document.getElementById('progress_bar').className = 'loading';
};
reader_.onload = function(e) {
// Ensure that the progress bar displays 100% at the end.
progress.style.width = '100%';
progress.textContent = '100%';
setTimeout("document.getElementById('progress_bar').className='';", 2000);
}
// Read in the image file as a binary string.
reader_.readAsBinaryString(evt.target.files[0]);
}
document.getElementById('files6').addEventListener('change', handleFileSelect, false);
</script>
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