In Javascript, how can I perform a global replace on string with a variable inside '/' and '/g'?

I want to perform a global replace of string using String.replace in Javascript.

In the documentation I read that I can do this with /g, i.e. for example;

var mystring = mystring.replace(/test/g, mystring);

and this will replace all occurrences inside mystring. No quotes for the expression.

But if I have a variable to find, how can I do this without quotes?

I've tried something like this:

var stringToFind = "test";

//first try

mystring = mystring.replace('/' + stringToFind + '/g', mystring);

//second try, not much sense at all

mystring = mystring.replace(/stringToFind/g, mystring);

but they don't work. Any ideas?