# Extending Charles with your own Javascript

You can add your own JS to execute within an active tab and also pass values back to bubble. Please have a look at this tutorial: <https://share.descript.com/view/NARVH1XDUbL>

**Code snippet**

```javascript
//send message to parent window
var msg = {
    "requestType":"customFunction"
}
window.parent.postMessage(JSON.stringify(msg), "*");


//listening for messages from the parent window
window.addEventListener('message', function (event) {
    // create object from event.data
    eventdata = JSON.parse(event.data);
    if (eventdata.returnType == "h1") {
        console.log('Received h1: ', eventdata.value);
    }
}, false);
```


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