Referenceerror: resizeobserver is not defined

The reference error “resizeobserver is not defined” occurs when the ResizeObserver class is used without it being defined first. The ResizeObserver is a feature of the JavaScript programming language that allows developers to observe changes to the size of an element. It is widely used for responsive designs, where elements need to adapt to different screen sizes or browser window dimensions.

To resolve this error, you need to ensure that the ResizeObserver class is available, which requires the following:

• First, check if your browser supports the ResizeObserver natively. You can do this by checking the global object for the existence of the ResizeObserver class:

  if ('ResizeObserver' in window) {
    // ResizeObserver is supported
  } else {
    // ResizeObserver is not supported, you may need a polyfill
  }
        

• If the browser doesn’t support the ResizeObserver natively, you need to include a polyfill library to provide support. A polyfill is a piece of code that brings a new feature to older browsers that do not natively support it. An example of a popular ResizeObserver polyfill is from the “resize-observer-polyfill” library. You can include it in your HTML file using a script tag:

  <script src="https://cdn.jsdelivr.net/npm/resize-observer-polyfill@1.5.1/ResizeObserver.polyfill.min.js"></script>
        

  This script should be included before any code that uses the ResizeObserver class.

By checking if the browser supports the ResizeObserver and including a polyfill when necessary, you can ensure that the “resizeobserver is not defined” error is resolved.