是否有窗口获取焦点的浏览器事件？ [英] Is there a browser event for the window getting focus?

问题描述

有没有办法在我点击浏览器并给予关注时，运行一次方法？然后当浏览器失去焦点然后重新获得焦点再次再次运行该方法时。

Is there a way that when I click on my browser, and give it focus, to run a method once? And then when the browser loses focus and then gets the focus back to again run that method only once, again.

推荐答案

你可以在窗口对象上附加 focus 和 blur 事件处理程序跟踪窗口是否获得或失去焦点（请参阅 http://jsfiddle.net/whQFz/ 以获取一个简单的示例）。 window 适用于当前浏览器上下文（因此可以是窗口，选项卡，框架等）。

You can attach focus and blur event handlers on the window object to track if the window gets or loses focus (see http://jsfiddle.net/whQFz/ for a trivial example). window applies to the current browser context (so that could be a window, a tab, a frame, etc.).

注意：每次窗口获得焦点时，焦点事件都会触发，模糊事件会在每次失去焦点时触发。将焦点从窗口移开的一个示例是 alert 窗口。如果您尝试在 onfocus 事件处理程序中发出警报，您将获得无限循环警报！

Note : The focus event will fire every time the window gets focus and the blur event will fire every time it loses focus. An example of something that takes focus away from the window is an alert window. If you try to alert in an onfocus event handler you'll get an infinite loop of alerts!

// Set global counter variable to verify event instances
var nCounter = 0;

// Set up event handler to produce text for the window focus event
window.addEventListener("focus", function(event) 
{ 
    document.getElementById('message').innerHTML = "window has focus " + nIndex; 
    nCounter = nCounter + 1; 
}, false);

// Example of the blur event as opposed to focus
// window.addEventListener("blur", function(event) { 
// document.getElementById('message').innerHTML = "window lost focus"; }, 
// false);

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