What happened on the mobile browser?

I’ve published a React web on the Github page.And there was something happened. I wanted to use the window object, so I need to check if it exist and did the below code.

const isBrowser = () => typeof window !== "undefined"

and print in the <div>{isBrowser() ? "true" : "false"}</div>

and then I checked the result on macbook's Google Chrome. It was true.
But when I checked it on my iphone's Google Chrome. It was false.