Handling special characters in Java script to enclose them in Square Brackets?

Question

I am trying to write a Java Script function that should enclose all the special characters in the given String in a bracket like following -

Input ===> Output

123@#$, ====> 123[@][#][$][,]

Changing All the special characters to certain String [ _ in this case] is easy -

string = string.replace(/[^a-zA-Z0-9]/g,'_');