JAVASCRIPT

detect paste in textarea

function getTextAreaSelection(textarea) {
    var start = textarea.selectionStart, end = textarea.selectionEnd;
    return {
        start: start,
        end: end,
        length: end - start,
        text: textarea.value.slice(start, end)
    };
}

function detectPaste(textarea, callback) {
    textarea.onpaste = function() {
        var sel = getTextAreaSelection(textarea);
        var initialLength = textarea.value.length;
        window.setTimeout(function() {
            var val = textarea.value;
            var pastedTextLength = val.length - (initialLength - sel.length);
            var end = sel.start + pastedTextLength;
            callback({
                start: sel.start,
                end: end,
                length: pastedTextLength,
                text: val.slice(sel.start, end)
            });
        }, 1);
    };
}

var textarea = document.getElementById("your_textarea");
detectPaste(textarea, function(pasteInfo) {
    alert(pasteInfo.text);
    // pasteInfo also has properties for the start and end character
    // index and length of the pasted text
});