Javascript OnPaste

问题:

I have this right now:

<input type="text" placeholder="Paste text" onPaste="alert(this.value);">

This does infact work, except, it returns a blank alert window. I don't get any value. Help?

回答1:

The onpaste event fires before the input's value is changed. You need something such as a setTimeout:

<input type="text" placeholder="Paste text" onPaste="var e=this; setTimeout(function(){alert(e.value);}, 4);">​

I'm storing a reference to this inside a global var as this is not accessible inside the scope of a timeout function which is attached to the window object.

I'm using 4 miliseconds as the Timeout as it's the minimum valid Interval/Timeout in the HTML5 specification. Edit: As noted in the comments, you may also use 0 miliseconds as timeOut which is automatically recalculated to 4. jsPerf tests.

Fiddle

You may as well use a function call inside your onpaste event passing this as a parameter to prevent your HTML mixing with JS too much. :)

And here's a function easier to read and which you can use in multiple inputs:

function pasted(element) {
    setTimeout(function(){
        alert(element.value);
    }, 0); //or 4
}​

Which can be called with simply onPaste="pasted(this)" for any input.

Fiddle

回答2:

This is because the onpaste event fires before the content gets pasted into the element (link) so it's not there yet at the time you handle it.

Modern browsers support methods of obtaining clipboard data inside the event handler. Refer to JavaScript get clipboard data on paste event (Cross browser) for cross-browser solution attempts.

Also, you can always work around your issue by simply starting a timer in the event handler function (10ms should be enough) that would check your input value later.