jQuery Uncaught TypeError: Cannot read property 'fn' of undefined (anonymous function)

All, I'm getting an error from some of my code that I downloaded. Here is the code:

/*----------------------------------------------------------------------*/
/* wl_Alert v 1.1 
/* description: Handles alert boxes
/* dependency: jquery UI Slider, fadeOutSlide plugin
/*----------------------------------------------------------------------*/


$.fn.wl_Alert = function (method) {
var args = arguments;
return this.each(function () {

    var $this = $(this);


    if ($.fn.wl_Alert.methods[method]) {
        return $.fn.wl_Alert.methods[method].apply(this, Array.prototype.slice.call(args, 1));
    } else if (typeof method === 'object' || !method) {
        if ($this.data('wl_Alert')) {
            var opts = $.extend({}, $this.data('wl_Alert'), method);
        } else {

            var opts = $.extend({}, $.fn.wl_Alert.defaults, method, $this.data());
        }
    } else {
        $.error('Method "' + method + '" does not exist');
    }


    if (!$this.data('wl_Alert')) {

        $this.data('wl_Alert', {});

        //bind click events to hide alert box
        $this.bind('click.wl_Alert', function (event) {
            event.preventDefault();

            //Don't hide if it is sticky
            if (!$this.data('wl_Alert').sticky) {
                $.fn.wl_Alert.methods.close.call($this[0]);
            }

            //prevent hiding the box if an inline link is clicked
        }).find('a').bind('click.wl_Alert', function (event) {
            event.stopPropagation();
        });
    } else {

    }
    //show it if it is hidden
    if ($this.is(':hidden')) {
        $this.slideDown(opts.speed / 2);
    }

    if (opts) $.extend($this.data('wl_Alert'), opts);
});

};

$.fn.wl_Alert.defaults = {
speed: 500,
sticky: false,
onBeforeClose: function (element) {},
onClose: function (element) {}
};
$.fn.wl_Alert.version = '1.1';


$.fn.wl_Alert.methods = {
close: function () {
    var $this = $(this),
        opts = $this.data('wl_Alert');
    //call callback and stop if it returns false
    if (opts.onBeforeClose.call(this, $this) === false) {
        return false;
    };
    //fadeout and call an callback
    $this.fadeOutSlide(opts.speed, function () {
        opts.onClose.call($this[0], $this);
    });
},
set: function () {
    var $this = $(this),
        options = {};
    if (typeof arguments[0] === 'object') {
        options = arguments[0];
    } else if (arguments[0] && arguments[1] !== undefined) {
        options[arguments[0]] = arguments[1];
    }
    $.each(options, function (key, value) {
        if ($.fn.wl_Alert.defaults[key] !== undefined || $.fn.wl_Alert.defaults[key] == null) {
            $this.data('wl_Alert')[key] = value;
        } else {
            $.error('Key "' + key + '" is not defined');
        }
    });

}
};

//to create an alert box on the fly
$.wl_Alert = function (text, cssclass, insert, after, options) {
//go thru all
$('div.alert').each(function () {
    var _this = $(this);
    //...and hide if one with the same text is allready set
    if (_this.text() == text) {
        _this.slideUp($.fn.wl_Alert.defaults.speed);
    }
});

//create a new DOM element and inject it
var al = $('<div class="alert ' + cssclass + '">' + text + '</div>').hide();
(after) ? al.appendTo(insert).wl_Alert(options) : al.prependTo(insert).wl_Alert(options);

//return the element
return al;
};

Has anyone seen this type of error before? How would I resolve something like this? Thanks for any advice you have!

Solution 1:

try to call jQuery library before bootstrap.js

<script src="js/jquery-3.3.1.min.js"></script>
<script src="js/bootstrap.min.js"></script>

Solution 2:

Try this:

(function ( $ ) { 

    // put all that "wl_alert" code here   

}( jQuery ));

So, the $ variable is apparently corrupted, but the jQuery variable should still refer to the jQuery object. (In normal circumstances, both the $ and jQuery variables refer to the (same) jQuery object.)

Instead of having to replace the $ name with the jQuery name in your entire code, you can simply use an IIFE to alias the name manually. So, the outside-variable jQuery is aliased with the $ variable inside the function.

Here's a simple example to help you understand this concept:

var foo = 'Peter';

(function ( bar ) {

    bar // evaluates to 'Peter'

}( foo ));

Solution 3:

If you get Cannot read property 'fn' of undefined, the problem may be you loading libraries in wrong order.

For example:

You should load bootstrap.js first and then load bootstrap.js libraries.

<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/js/bootstrap.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/bootstrap3-dialog/1.34.7/js/bootstrap-dialog.min.js"></script>