Passing regex modifier options to RegExp object

Question

I am trying to create something similar to this:

var regexp_loc = /e/i;

except I want the regexp to be dependent on a string, so I tried to

Answer 1

Want to share an example here:

I want to replace a string like: hi[var1][var2] to hi[newVar][var2]. and var1 are dynamic generated in the page.

so I had to use:

var regex = new RegExp("\\\\["+var1+"\\\\]",'ig');
mystring.replace(regex,'[newVar]');

This works pretty good to me. in case anyone need this like me. The reason I have to go with [] is var1 might be a very easy pattern itself, adding the [] would be much accurate.