I am doing some testing on cross domain comunication, i would want to do the testing directly into chrome inspection rather than keep deploying my script to dev environment. Assuming have only 2 page ,

localhost:8766 and localhost:8765
localhost8765 is where i have declared to PostMessage
localhost8766 is the receiver

On Chrome browser , i have selected : devtableau.html as per below image where displaying the message is declared.

This is working perfectly fine but what im trying to achieve is to declare the window.addeventlistener directly to chrome inspect element to do some testing

when i place window.addevenlistener directly to chrome , its returning undefined ,

What is the correct approach in doing this ?