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Mastering Cross-Origin Communication in JavaScript with window.postMessage()

Sumit kumar Singh
JavaScript in Plain English
5 min readSep 6, 2024

To understand the usage of window.postMessage() in JavaScript, it's crucial to grasp what the method does and why it's important in modern web development, especially in handling cross-origin communication between different windows, iframes, or tabs. This technique is commonly used to allow secure and controlled interaction between different origins, vital in a web ecosystem where security is paramount.

In this explanation, we’ll cover:

  1. What is window.postMessage()?
  2. Why is it necessary?
  3. How to use it?
  4. Security considerations
  5. Examples and use cases

1. What is window.postMessage()?

The window.postMessage() method is part of the HTML5 Web Messaging API, enabling cross-origin communication between different browsing contexts, such as iframes, windows, or tabs. The method allows scripts from one origin to send asynchronous messages to another origin, bypassing the same-origin policy, which typically restricts how documents or scripts loaded from one origin can interact with resources from another origin.

The method signature looks like this:

window.postMessage(message…

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Published in JavaScript in Plain English

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Written by Sumit kumar Singh

YouTube: https://shorturl.at/8zZ4B Topmate: https://topmate.io/sumit_kr_singh 📚 HTML, Angular, React, and JavaScript 🧑‍💻 Tips & tricks

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