onmessage HTML Attribute

The "onmessage" attribute in HTML is an event attribute that can be added to an element, that when triggered, runs a script when a message is received by the element. It's typically used with the postMessage API, which allows communication between different windows or frames on a website. The attribute value is a string containing the JavaScript code that should be executed when the event is fired.

For example, in the following code snippet, the onmessage attribute is used to listen for messages sent to a specific iframe:


<iframe src="example.com" onmessage="alert(event.data)"></iframe>

The onmessage attribute can be used on elements such as iframes, windows and workers to listen for messages sent by other scripts. It's useful to establish communication between different parts of a web application, or to facilitate cross-origin communication.

It's worth noting that the onmessage attribute is widely supported by all modern browsers, and also it is a standard attribute, which means it is part of the official HTML specification.

In summary, the "onmessage" attribute in HTML is an event attribute that can be added to an element, that when triggered, runs a script when a message is received by the element. It's typically used with the postMessage API, which allows communication between different windows or frames on a website. It can be used on elements such as iframes, windows and workers to listen for messages sent by other scripts. It's useful to establish communication between different parts of a web application, or to facilitate cross-origin communication. It is widely supported and is a standard attribute, which means it is part of the official HTML specification.