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• 句法
• 范例
• Reduced time precision
• 规范
• 浏览器兼容性
• 另请参阅
• 相关话题

File.lastModified read-only property provides the last modified date of the file as the number of milliseconds since the Unix epoch (January 1, 1970 at midnight). Files without a known last modified date return the current date.

句法

const time = instanceOfFile.lastModified;
					

值

A number that represents the number of milliseconds since the Unix epoch.

范例

Reading from file input

<input type="file" multiple id="fileInput">
					

const fileInput = document.querySelector('#fileInput');
fileInput.addEventListener('change', (event) => {
  // files is a FileList object (similar to NodeList)
  const files = event.target.files;
  for (let file of files) {
    const date = new Date(file.lastModified);
    console.log(`${file.name} has a last modified date of ${date}`);
  }
});
					

Try the results out below:

Dynamically created files

If a File is created dynamically, the last modified time can be supplied in the new File() constructor function. If it is missing, lastModified inherits the current time from Date.now() at the moment the File object gets created.

const fileWithDate = new File([], 'file.bin', {
  lastModified: new Date(2017, 1, 1),
});
console.log(fileWithDate.lastModified); //returns 1485903600000
const fileWithoutDate = new File([], 'file.bin');
console.log(fileWithoutDate.lastModified); //returns current time
					

Reduced time precision

To offer protection against timing attacks and fingerprinting, the precision of someFile.lastModified might get rounded depending on browser settings.
In Firefox, the privacy.reduceTimerPrecision preference is enabled by default and defaults to 20us in Firefox 59; in 60 it will be 2ms.

// reduced time precision (2ms) in Firefox 60
someFile.lastModified;
// 1519211809934
// 1519211810362
// 1519211811670
// ...
// reduced time precision with `privacy.resistFingerprinting` enabled
someFile.lastModified;
// 1519129853500
// 1519129858900
// 1519129864400
// ...
					

In Firefox, you can also enabled privacy.resistFingerprinting , the precision will be 100ms or the value of privacy.resistFingerprinting.reduceTimerPrecision.microseconds , whichever is larger.

规范

规范	状态	注释
文件 API The definition of 'lastModified' in that specification.	工作草案	初始定义。

浏览器兼容性

The compatibility table on this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request. 更新 GitHub 上的兼容性数据

	桌面						移动
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet
lastModified	Chrome 13	Edge 18	Firefox 15	IE No	Opera 16	Safari 10	WebView Android Yes	Chrome Android Yes	Firefox Android No	Opera Android No	Safari iOS 10	Samsung Internet Android Yes

图例

完整支持

完整支持

不支持

不支持

另请参阅

• File

元数据

• 最后修改： Feb 8, 2020

相关话题

1. File
2. 构造函数

   1. File()
3. 特性

   1. fileName
   2. fileSize
   3. lastModified
   4. lastModifiedDate
   5. mozFullPath
   6. 名称
   7. type
   8. webkitRelativePath
4. 方法

   1. getAsBinary()
   2. getAsDataURL()
   3. getAsText()
5. 继承：

   1. Blob