javascript prevent copy/pasting beyond character limit in textarea

问题

I have the following code (pulled from this question) for setting a character limit on textareas.

function maxLength(el) {    
    if (!("maxLength" in el)) {
        var max = el.attributes.maxLength.value;
        el.onkeypress = function () {
            if (this.value.length >= max) return false;
        };
    }
}

var maxtext = document.getElementsByClassName("maxtext");

for (var i = 0; i < maxtext.length; i++) {
    maxLength(maxtext[i]);
}

And an example of my html for textareas:

<textarea maxlength="150" class="maxtext"></textarea>

This all works just fine in Firefox and Chrome. In IE7+, it will stop me if I type up to the limit, but I'm then able to copy/paste text without restriction.

Any way to modify this script to prevent copy/pasting beyond the max character limit?

回答1:

Listen for the onpaste event. Once the event fires, grab the text from the clipboard and manipulate it how you like.

HTML

<textarea id="test" maxlength="10" class="maxtext"></textarea>

JAVASCRIPT

var test = document.getElementById("test");

test.onpaste = function(e){
    //do some IE browser checking for e
    var max = test.getAttribute("maxlength");
    e.clipboardData.getData('text/plain').slice(0, max);
};

EXAMPLE

回答2:

You could listen to the onchange event to check the content length, if exceeds the limit then subtract it.

来源：https://stackoverflow.com/questions/15573561/javascript-prevent-copy-pasting-beyond-character-limit-in-textarea