jquery to make chain triger of alt + printpant then to dump image on canvas

I'm trying to create a button for bug reports: and I need to improve the code script to execute the following functions:

Javascript code (Jquery):

$(function() {
    $(document).on("click",'[id^="button-test"]', function (event, xhr, settings) {
        console.log('event trigger');
        var e = jQuery.Event("keydown");
        e.which = 44;       // # PrintScreen code value
        e.altKey = true;     // Alt key pressed
        $("input").trigger(e);

            retrieveImageFromClipboardAsBlob(e, function(imageBlob){
                if(imageBlob){
                    var canvas = document.getElementById("mycanvas");
                    var ctx = canvas.getContext('2d');
                    var img = new Image();
                    img.onload = function(){
                        canvas.width = this.width;
                        canvas.height = this.height;
                        ctx.drawImage(img, 0, 0);
                    };
                    var URLObj = window.URL || window.webkitURL;
                    img.src = URLObj.createObjectURL(imageBlob);
                }
            });

    });
});
function retrieveImageFromClipboardAsBlob(pasteEvent, callback){
    if(pasteEvent.clipboardData == false){
        if(typeof(callback) == "function"){
            callback(undefined);
        }
    };
    var items = pasteEvent.clipboardData.items;
    if(items == undefined){
        if(typeof(callback) == "function"){
            callback(undefined);
        }
    };
    for (var i = 0; i < items.length; i++) {
        // Skip content if not image
        if (items[i].type.indexOf("image") == -1) continue;
        // Retrieve image on clipboard as blob
        var blob = items[i].getAsFile();
        if(typeof(callback) == "function"){
            callback(blob);
        }
    }
}

HTML Code:

<span>
    <button id="button-test">prueba</button>
</span>
<canvas style="border:1px solid grey;" id="mycanvas">

Errors:

Uncaught TypeError: Cannot read property 'items' of undefined

and refers to this line,

var items = pasteEvent.clipboardData.items;

I do not know what I'm doing wrong