TextTrackList.length

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只读 TextTrackList property length returns the number of entries in the TextTrackList , each of which is a TextTrack representing one track in the media element. A value of 0 indicates that there are no text tracks in the media.

句法

var trackCount = TextTrackList.length;

值

A number indicating how many text tracks are included in the TextTrackList . Each track can be accessed by treating the TextTrackList as an array of objects of type TextTrack .

范例

This snippet gets the number of text tracks in the first media element found in the DOM by querySelector() .

var mediaElem = document.querySelector("video, audio");
var numTextTracks = 0;
if (mediaElem.textTracks) {
  numTextTracks = mediaElem.textTracks.length;
}

Note that this sample checks to be sure HTMLMediaElement.textTracks is defined, to avoid failing on browsers without support for TextTrack .

规范

规范	状态	注释
HTML 实时标准 The definition of 'TextTrackList: length' in that specification.	实时标准

浏览器兼容性

The compatibility table in 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
`length`	Chrome 44	Edge ≤18	Firefox Yes	IE ?	Opera 31	Safari 10	WebView Android 44	Chrome Android 44	Firefox Android ?	Opera Android 32	Safari iOS ?	Samsung Internet Android 4.0

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完整支持
兼容性未知 ?

元数据

最后修改： May 31, 2019

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