Typeerror: mutationobserver is not a constructor

April 27, 2023April 27, 2023 by john paul blauro

Are you looking for a solution to fix the “Typeerror: mutationobserver is not a constructor” error in your codes?

Then this article is for you.

In this article, we will discuss the possible causes of this error, and give solutions to resolve this error.

But first, let’s discuss what this error means.

What is Typeerror: mutationobserver is not a constructor?

The “Typeerror: mutationobserver is not a constructor” error message occurs in JavaScript when attempting to use the MutationObserver constructor to create a new object.

But for some reason, the MutationObserver constructor is not available.

What is mutationobserver?

The MutationObserver constructor is a built-in object in the browser’s JavaScript environment that allows developers to observe changes to the DOM.

Why Typeerror: mutationobserver is not a constructor occurs?

Typeerror: mutationobserver is not a constructor occurs for several reasons, such as:

Outdated web browser

Conflicts with other code
Limitations of the environment

1. Outdated web browser:

The MutationObserver constructor is not supported in older versions of web browsers.

If the code is running in an outdated browser, it may not be able to find the constructor, resulting in an error.

2. Conflicts with other code:

If there is other JavaScript code running on the same web page that is redefining or overwriting the MutationObserver constructor, conflicts may arise.

It prevents the constructor from being called correctly.

Here’s an example:

// Redefining the MutationObserver constructor
var MutationObserver = function() {
    console.log("Custom MutationObserver constructor");
};

// Attempting to create a new instance of the MutationObserver constructor
var observer = new MutationObserver(function(mutations) {
    mutations.forEach(function(mutation) {
        console.log(mutation);
    });    
});

observer.observe(document, { childList: true });

In this example, it redefines the MutationObserver constructor.

Replacing it with a custom function that logs a message to the console.

The code attempts to create a new instance of the MutationObserver constructor.

Then calls the observe() method on the observer object.

It cannot find the original MutationObserver constructor and instead uses the custom function.

As a result, the error message displayed:

Typeerror: mutationobserver is not a constructor

Because the custom function is not a valid constructor for the MutationObserver object.

3. Limitations of the environment:

The MutationObserver constructor may not be available in some environments.

Such as Node.js or other non-browser environments, leading to the error.

Here’s an example code snippet:

const { JSDOM } = require("jsdom");

const dom = new JSDOM(`<!DOCTYPE html><p>Hello world</p>`);
const document = dom.window.document;

var observer = new MutationObserver(function(mutations) {
    mutations.forEach(function(mutation) {
        console.log(mutation);
    });    
});

observer.observe(document, { childList: true });

In this example, the code above is running in an environment such as Node.js.

It does not support the MutationObserver constructor, the reason why the error message is displayed.

Typeerror: mutationobserver is not a constructor – Solutions
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Here are some solutions to fix the “Typeerror: mutationobserver is not a constructor” error:

Solution 1. Update your web browser:

MutationObserver is supported in most modern web browsers, including Google Chrome, Mozilla Firefox, and Microsoft Edge.

Here is an example code that checks if the MutationObserver constructor is supported in the current web browser:

// Check if MutationObserver is supported
if (typeof MutationObserver === "undefined") {
    // Display an error message or redirect to an error page
    console.error("Your web browser does not support MutationObserver.");
}

In this example, If the constructor is undefined, the code displays an error message in the console or redirects the user to an error page.

To update your Web Browser follow these steps:

Open your web browser (e.g. Google Chrome, Mozilla Firefox, Safari, etc.).
Click on the three-dot or three-line icon in the top right corner of the browser window.
Click on “Settings” or “Preferences” from the drop-down menu.

Scroll down to the “About” or “Help” section of the settings page.
Click on the “Check for updates” or “Update” button.
If an update is available, follow the prompts to download and install the update.

Once the update is complete, restart your web browser to apply the changes.

Solution 2. Avoid redefining the MutationObserver constructor:

Ensure that you are not redefining the MutationObserver constructor in your code or in any external scripts that may be running on the page.

Here is an example code that checks if the MutationObserver constructor has already been defined in the current web page or script:

// Check if MutationObserver has already been defined
if (typeof MutationObserver !== "undefined") {
    console.warn("MutationObserver has already been defined.");
} else {
    // Define the MutationObserver constructor
    var MutationObserver = function() {
        // Custom constructor code
    };
}

In this example, If the constructor has not been defined, the code defines a new constructor with custom code.

If the constructor has already been defined, the code displays a warning message in the console and does not redefine the constructor.

Solution 3. Use a polyfill:

If you need to support older web browsers that do not support the MutationObserver constructor, you can use a polyfill like MutationObserver-shim or mutationobserver-polyfill.

These polyfills simulate the behavior of the MutationObserver constructor using other methods.

It allows you to use the constructor in older web browsers.

Here is an example:

// Include the mutationobserver-polyfill library
<script src="mutationobserver-polyfill.js"></script>

// Create a new instance of MutationObserver
var observer = new MutationObserver(function(mutations) {
    mutations.forEach(function(mutation) {
        console.log(mutation);
    });
});

// Observe changes to the DOM
observer.observe(document, { childList: true });

This example includes the mutationobserver-polyfill library.

Which provides a polyfill for the MutationObserver constructor in older web browsers.

Then, it creates a new instance of the constructor and calls the observe() method to monitor changes to the DOM.

Solution 4. Check your environment:

If you’re running JavaScript code in an environment that does not support the MutationObserver constructor you may need to use a different method for observing DOM mutations.

For example, you could use the MutationEvents API in older web browsers, or use a different library or framework that provides similar functionality.

Just like the example below:

// Check if running in Node.js environment
if (typeof window === "undefined") {
    console.error("MutationObserver is not supported in Node.js.");
} else {
    // Create a new instance of MutationObserver
    var observer = new MutationObserver(function(mutations) {
        mutations.forEach(function(mutation) {
            console.log(mutation);
        });
    });
    
    // Observe changes to the DOM
    observer.observe(document, { childList: true });
}

In this example it checks if the JavaScript code is running in a Node.js environment, which does not support the MutationObserver constructor.

If running in Node.js, the code displays an error message in the console.

If running in a web browser environment, the code creates a new instance of the constructor and calls the observe() method to monitor changes to the DOM.

So those are the different ways to fix “Typeerror: mutationobserver is not a constructor”.

Hope that one or more of them helps you troubleshoot and resolve the error.

Here are the other fixed errors that you can visit, you might encounter them in the future.

typeerror: bad operand type for unary -: str

Conclusion

In conclusion, The “Typeerror: mutationobserver is not a constructor” is an error message that occurs in JavaScript when attempting to use the MutationObserver constructor to create a new object.

To solve this error, you can try to update your browser, avoid redefining the MutationObserver constructor, use a polyfill, or check your environment.

By following the given solution above, surely you can fix the error quickly and proceed to your coding project again.

I hope this article helps you to solve your problem regarding a Typeerror stating “mutationobserver is not a constructor”.

We’re happy to help you.

Happy coding! Have a Good day and God bless.