How to detect which userscript manager is running the script

Question

I'm using a function in a userscript that I'm writing which does not work in Greasemonkey due to the limitations of Greasemonkey. This function is not necessary for proper operation of the userscript, but it improves user experience, so I don't want to just remove it entirely.

I tried using a try { ... } catch() { ... } block, but unfortunately Greasemonkey ceases execution of the script as soon as it attempts execution of the function instead of throwing an exception. So I instead decided to prevent execution of the function when the script is loaded via Greasemonkey, but I have been unable to find a method of doing that.

• I've read through the API reference, but was unable to find anything useful.
• I found this github issue that would allow detection of Greasemonkey but that seems to have been "fixed" now.
• I looked through this topic on userscripts-mirror.org, but the proposed solution in that thread checks for the existence of GM* functions, which are also available in most other userscript managers (specifically Tampermonkey and Violentmonkey which support the function that Greasemonkey does not).

How can I go about detecting whether the active userscript manager is Greasemonkey or not?

Answer 1

Checking what manager is running is a poor approach, which will prove to be brittle and high maintenance. The smart thing to do is to check if this mysterious function exists, or works as needed.

This is the same type of problem as "browser sniffing" and the answer is the same: Use feature detection instead.
EG:

if (typeof dicyFunc == "function") {
    //-- Use the function
    dicyFunc ();
}
else {
    console.error ("This userscript engine does not support dicyFunc.");
}

Update for user comment: Sometimes you might also need a try... catch block. EG:

try {
    REALLY_dicyFunc ();
}
catch (zError) {
    console.error ("REALLY_dicyFunc fail on this engine: ", zError);
}

You need to give a concrete example (Make an MCVE) for more.

---

If you insist on engine detection, then see this answer to a near duplicate question. Essentially, you would use GM_info.scriptHandler property, possibly backed up by the GM_info.version property.

For best results, make a feature request for Greasemonkey to support the scriptHandler property. (Tampermonkey and ViolentMonkey already do.) There is a recently closed pull request for this for Greasemonkey, so maybe it will be in the next version?