Error: Unable to access undefined properties while trying to read 'add' value. Issue identified in the code related to "classlist.add" function

I am currently facing an issue where I receive the error message: Uncaught TypeError: Cannot read properties of undefined (reading 'add') when trying to add a class to a div using a button.

After researching on Stack Overflow, I stumbled upon a thread with a similar problem. Here is my simplified code:

<!DOCTYPE html>
<html lang="en">
<body>
    <div class="name-row">Hello!</div>
    <button type="button" onclick="clear()" id="clearButton">Clear</button>
    
    <script>
        document.getElementById('clearButton').addEventListener('click', function () {
                let allNamesElm = document.getElementsByClassName("name-row");
                allNamesElm.classList.add("showing");
                window.alert("Cleared!");
                console.log("cleared");
            });
    </script>
</body>
</html>

Despite attempting to explicitly call the function, the code does not execute as expected:

<!DOCTYPE html>
<html lang="en">
<body>
    <div class="name-row">Hello!</div>
    <button type="button" onclick="clear()" id="clearButton">Clear</button>
    
    <script>
        function clear() {
                let allNamesElm = document.getElementsByClassName("name-row");
                allNamesElm.classList.add("showing");
                window.alert("Cleared!");
                console.log("cleared");
            };
    </script>
</body>
</html>

It seems like a simple mistake, but despite my efforts to correct it, the issue persists. Any help would be greatly appreciated!

Answer №1

It's important to note that the variable allNamesElm is not a single element, but rather an HTMLCollection which behaves like an array. To target a specific element, you should access the first item in the collection.

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