IS_BROWSER fails when application is not built/served by Webpack

[fabioimpe]

Hi,
I'm facing an issue where in a browser environment MQTT library still try to use ws instead of the browser native WebSocket for the web socket connection.
After digging in the codebase I found out that the following code to understand if the code is running on node or in a browser is NOT taking care of any bundler other than Webpack (for instance I'm on Parcel 2 and is not working):

MQTT.js/lib/connect/ws.js

Line 18 in b3ce3da

const IS_BROWSER = (typeof process !== 'undefined' && process.title === 'browser') || typeof __webpack_require__ === 'function'

In addition to this I don't understand the usage of process.title at all, I investigated a bit about this but I wasn't able to find any meaningful documentation or hint of its usage.

I think is worth having a safer way to check whether the code is running on the browser or not.

[fabioimpe]

Maybe related issues:
#1233
#1412
#1523
#1441

[robertsLando]

Fixed by #1571