Window.top

返回窗口层级最顶层窗口的引用。

语法

var topWindow = window.top;

window.parent 返回当前窗口的直接父对象，而 window.top 返回最顶层的窗口对象。

当你在处理父窗口的子框架（subframe），而你想获取顶层框架时，这个属性相当有用。

Specification	Status	Comment
HTML Living Standard window.top	Living Standard
HTML5 window.top	Recommendation	Initial definition

	Desktop						Mobile
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet
`top`	Chrome Full support 1	Edge Full support 12	Firefox Full support 1 Notes Full support 1 Notes Notes Starting in Firefox 6, this property is read only, as defined by the standard.	IE Full support 4	Opera Full support ≤12.1	Safari Full support 3	WebView Android Full support 1	Chrome Android Full support 18	Firefox Android Full support 4	Opera Android Full support ≤12.1	Safari iOS Full support 1	Samsung Internet Android Full support 1.0