绑定 <svelte:window>到`onbeforeunload` [英] Bind &lt;svelte:window&gt; to `onbeforeunload`

问题描述

我希望绑定到 但没有成功.

<!-- 不起作用 --><svelte:window on:beforeunload={() =>真}/><!-- 不起作用--><svelte:window on:onbeforeunload={() =>真}/><!-- 不起作用--><svelte:window on:beforeUnload={() =>真}/>

在所有情况下，window.onbeforeunload 都是 null

我最后只用了 window.onbeforeunload = () =>对 但想知道为什么在元素上设置不起作用.

解决方案

使用svelte:window

时需要设置事件returnValue

<svelte:window on:beforeunload={beforeUnload}/>

这样做的原因是在svelte中写on:event={handler}，等价于写node.addEventListener(event, handler, options)>

事实证明，当使用 addEventListener 附加 beforeunload 时，然后 你需要设置事件returnValue和/或返回一个值

<块引用>

但是请注意，并非所有浏览器都支持此方法，有些浏览器而是要求事件处理程序实现两个遗留问题之一方法:

• 为事件的 returnValue 属性分配一个字符串
• 从事件处理程序返回一个字符串.

使用window.onbeforeunload注册事件只需要返回值

I was hoping to bind to <svelte:window> but have no luck.

<!-- doesn't work -->
<svelte:window on:beforeunload={() => true} />

<!-- doesn't work -->
<svelte:window on:onbeforeunload={() => true} />

<!-- doesn't work -->
<svelte:window on:beforeUnload={() => true} />

in all instances, window.onbeforeunload is null

I ended up just going with window.onbeforeunload = () => true but was wondering why setting on the element didn't work.

解决方案

You need to set the event returnValue when using svelte:window

<script>

  function beforeUnload() {
    // Cancel the event as stated by the standard.
    event.preventDefault();
    // Chrome requires returnValue to be set.
    event.returnValue = '';
    // more compatibility
    return '...';
  }

</script>

<svelte:window on:beforeunload={beforeUnload}/>

The reason for this is that writing on:event={handler} in svelte, is equivalent to writing node.addEventListener(event, handler, options)

It turns out that when attaching beforeunload using addEventListener, then you need to set the event returnValue and/or return a value

However note that not all browsers support this method, and some instead require the event handler to implement one of two legacy methods:

• assigning a string to the event's returnValue property
• returning a string from the event handler.

Registering the event using window.onbeforeunload only requires a return value

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