document.getElementById("main").innerHTML not working

I have main.html, test.html and script.js in the same folder.  I'm using a Python package called Eel, and that's how I'm interacting with html and Javascript.  When I call function dummy() as shown below, I get a print statement from Python, which is exactly what I want, but when I change the "main" to "test" in the dummy() it doesn't print anything.  Why is that?  How come script.js knows about "main", but not about "test"?  

main.html
<div>
	<p id="main">This is from main.html</p>
	<input type="submit" name="" onclick="dummy()"></input>
<div>

test.html
<p id="test">This is p tag in test.html</p>

script.js
function dummy() {
	u = document.getElementById("main").innerHTML
	eel.dummy(u)
}