javascript - Why can the sessionStorage be saved when the onbeforeunload prompt box is closed and refreshed, but the alert cannot be played?

Question

http://www.runoob.com/jsref/e...

After hooking up.
Refresh it again
The function body will not be triggered at all.
I tested it. Why is this?
Just leave it unchecked

window.addEventListener("beforeunload", function(event) {
    alert("弹出");
    sessionStorage.name="你的名字";  //请教一下为什么这个sessionStorage都能存下来？而alert没弹出来？这是什么机制啊？ 
});

http://jsbin.com/zisazacani/e... JS Bin online example

Answer 1

Thanks for the invitation

Official documentation explains

Starting from May 25, 2011, the HTML5 specification states that in this event handler, calls to window.alert(), window.confirm(), and
window.prompt() will be ignored. See the HTML5 specification for details.

In addition, this is for security reasons and does not allow disabling system pop-ups.