An error message regarding JavaScript: 'Attempting to access a property that is undefined'

The code for javascript, html and css can be found working smoothly in this jsfiddle However, when the same code is placed into an HTML file like below:

<!doctype html>
<html>
  <head>
        <meta charset="utf-8">
        <meta http-equiv="X-UA-Compatible" content="chrome=1">
        <script src="http://ajax.aspnetcdn.com/ajax/jQuery/jquery-1.11.3.min.js"></script>
        <script type="text/javascript">
            var target = $(".mypara").offset().top;
            var interval = setInterval(function() {
                if ($(window).scrollTop() >= target) {
                    alert("made it!");
                    clearInterval(interval);
                    }
            }, 250);
        </script>
        <style>
            body {
            background-color: linen;
            height: 1000px;
            }
            p {
             color: blue;
              margin-top: 500px;
            }
        </style>

    </head>
    <body>
     <p class="mypara">asdfasdfasf</p>
    </body>
</html>

When viewed in the chrome console, the following error is displayed:

Uncaught TypeError: Cannot read property 'top' of undefined(anonymous function) @ index - Copy.html:8

This particular error pertains to line 8:

var target = $(".mypara").offset().top;

Are you able to assist in understanding why this error is occurring?

Answer №1

Make sure to properly wrap your code within the following block:

$(document).ready(function() {
    // insert your code here
});

If you attempt to access a DOM element before it has been created, this may result in errors as the class or item being targeted does not yet exist. To avoid this issue, ensure that your script is placed below the corresponding elements within the HTML structure.

When running your code in platforms such as JSFiddle, the functionality may work in this specific scenario due to how the code is encapsulated by default settings that rely on the DOM being fully loaded.

Answer №2

<!doctype html>
<html>
    <head>
        <meta charset="utf-8">
        <meta http-equiv="X-UA-Compatible" content="chrome=1">

        <style>
            body {
                background-color: linen;
                height: 1000px;
            }
            p {
                color: blue;
                margin-top: 500px;
            }
        </style>
    </head>

    <body>
        <p class="mypara">asdfasdfasf</p>
        <p class="mypara">Make sure to include JS files at the bottom so they are loaded accordingly.</p>
        <script src="http://ajax.aspnetcdn.com/ajax/jQuery/jquery-1.11.3.min.js"></script>
        <script type="text/javascript">
            // Execute code only when document is ready
            $(document).ready(function() {
                var target = $(".mypara").offset().top;
                var interval = setInterval(function() {
                    if ($(window).scrollTop() >= target) {
                        alert("made it!");
                        clearInterval(interval);
                    }
                }, 250);
            });

            </script>
    </body>
</html>

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