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Arthur Denner
Arthur Denner

Posted on • Originally published at arthurdenner.hashnode.dev

How to debug postMessages

TL;DR

monitorEvents(window, 'message')
// or
window.addEventListener('message', console.log)
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Concept

From the MDN docs:

The window.postMessage() method safely enables cross-origin communication between Window objects; e.g., between a page and a pop-up that it spawned, or between a page and an iframe embedded within it.

That's pretty cool, right?

Demo

Here is a demo of postMessage usage.

Debug

But how can we debug these messages?

Run the following in the Console tab:

// On Safari and Chromium-based browsers
monitorEvents(window, 'message')

// On Firefox
window.addEventListener('message', console.log)
// ^ It works in all the other browsers too
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If you're testing in CodeSandbox, run the command in the Console of its detached window.

Result

After the setup, when receiving messages, you should see something like this:

image.png

That's it!


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