Solve getElementsByTagName is not a function Error JavaScript

In this blog post, we’ll take a look at what to do when you get the error “getElementsByTagName is not a function” in your JavaScript code. We’ll discuss some possible causes of this error and offer some solutions that might help you fix it. Stay tuned!

how to solve javascript getelementsbytagname is not a function error

getElementsByTagName is not a function JavaScript

If you’re a JavaScript developer, you’ve probably run into the “getElementsByTagName is not a function” error at some point. This error can be caused by a number of things like –

  • Calling the getElementsByTagName method on a value that is not a proper DOM element.
  • Declaring the JS script before the value of the DOM element is declared.
  • Typo in the getElementsByTagName method. The method is case sensitive.

Let’s have a look at each of them in detail below. But, first let’s understand what this method actually does.

getElementsByTagName JavaScript

The getElementsByTagName function is used to retrieve a collection of all the DOM elements that match the specified tag name. It returns an HTMLCollection object consisting of matching tags.

The syntax of the method is as follows –

document.getElementsByTagName(tagname);

Where, tagname is the name of the HTML element you want to select. For example, if you want to retrieve all the <p> elements from a document, you would use the following code –

var p_elements = document.getElementsByTagName("p");

This would return an HTMLCollection of all the <p> elements in the document.

Now that we know what this method does, let’s look at some of the reasons why you might get the error “getElementsByTagName is not a function”.

1.getElementsByTagName Method Is Called On A Value That Is Not A Proper DOM Element

If you’re trying to call the getElementsByTagName method on a value that is not an actual DOM element, this is most likely the cause of your getElementsByTagName is not a function JavaScript error. For example, consider the HTML below –

<html>

<head>

</head>

<body>

<div class = “box”>

<p> This is box 1</p>

<p> This is box 2</p>

</div>

<div class = “box”>

<p> This is box 3</p>

<p> This is box 4</p>

</div>

<script>

const boxes = document.querySelectorAll(‘.box’);

console.log(boxes.getElementsByTagName(‘p’)); //returns error getElementsByTagName is not a function

</script>

</body>

</html>

If you try to call the getElementsByTagName method on one of these div elements, you’re likely to encounter an error since they are not actual DOM elements. To avoid this error, make sure that you are only calling the getElementsByTagName method on values that are proper DOM elements.

The below JavaScript code would work –

<script>

const boxes = document.querySelectorAll(‘.box’);

const firstBox = boxes.item(0);

console.log(firstBox.getElementsByTagName(‘p’)); //returns NodeList of <p> tags inside the first box

</script>

In the above code, we are using the querySelectorAll method to get all of the elements with the class name “box”. We then use the item method to get the first element from this NodeList and store it in a variable called firstBox. Now, when we call the getElementsByTagName method on firstBox, it works as expected and returns the NodeList of all <p> elements inside the first box.

The getElementsByTagName method can only be called on an actual DOM element, not on any other type of value. If you’re not sure if the value you’re trying to call the getElementsByTagName method on is an actual DOM element, you can use the instanceof operator to check.

For example, if we have a variable named “myElement” that might or might not be a DOM element, we can check it like this:

if(myElement instanceof Element){

// myElement is an actual DOM element

}else{

// myElement is NOT an actual DOM element

}

If you’re getting the getElementsByTagName is not a function error and you’ve confirmed that the value you’re trying to call it on is actually a DOM element, then this might be caused by another issue. Continue reading for more information.

2.Declaring The JS Script Before The Value Of The DOM Element Is Declared

If you’re trying to call the getElementsByTagName method on a value that is not an actual DOM element, you might also be getting this error because the JavaScript code or script where getElementsByTagName is called was declared before the value of the DOM element was declared.

For example, consider the code below –

<html>

<head>

</head>

<body>

<script>

const boxes = document.getElementsByClassName(‘box’);

console.log(boxes.getElementsByTagName(‘p’)); //returns error getElementsByTagName is not a function

</script>

<div class = “box”>

<p> This is box 1</p>

<p> This is box 2</p>

</div>

<div class = “box”>

<p> This is box 3</p>

<p> This is box 4</p>

</div>

</body>

</html>

In the above code, we have a <script> tag before the <div class=”box”> element. This means that the JavaScript code inside this <script> tag is executed before the actual DOM elements are declared and assigned values. So, when you try to call the getElementsByTagName method on the boxes variable that is declared inside a <script> tag, this error occurs since there are no actual DOM elements to query.

To avoid this issue, make sure you declare your JavaScript or script code after all of your actual DOM element values have been declared and assigned values. This will ensure that the getElementsByTagName method has valid values to call on when it is executed.

3.Typo In The getElementsByTagName Method

Another reason you might be getting this error is because of a typo in the getElementsByTagName method. If you mistakenly use the wrong case when typing the getElementsByTagName method, for example, GetElementsByTagName instead of getElementsByTagName or getElementByTagName instead of getElementsByTagName, then you might be getting this error.

This is because the method is case-sensitive and needs to be typed correctly in order for it to work properly. So, make sure you check the spelling and case of your getElementsByTagName method to ensure it is being called correctly.

Additionally, you can use a code editor to help find and correct any spelling or formatting errors in your scripts and methods.

Conclusion

There are several possible reasons you might be getting the “getElementsByTagName is not a function JavaScript” error, including declaring the JS script before the value of the DOM element, typing a typo in the getElementsByTagName method, or not using an actual DOM element.

To avoid this error, make sure you check the spelling and case of your getElementsByTagName method and that you’re using an actual DOM element when calling this method.

Additionally, if you’re getting this error because you declared your JavaScript code before the value of the DOM element was declared, try moving your script code to after all of your DOM element values have been declared. This should help resolve the issue.

If you’re still having trouble resolving this error, feel free to reach out to a professional programmer or developer for help troubleshooting and resolving the issue.

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