Question

What’s the intent of () inside the regex? Thanks.

pattern.replace(/\{(\d+)\}/g,
        function(pattern, index) { 
            return args[index].toString(); 
        });

PS: args is something like [“3”, “dl1”, “42”]

Answer 1

It is used to manage grouping.

The purpose of grouping is to make backreferences on searches & replaces. Using regex you can make that Jhon Doe becomes Doe, Jhon.

To achieve that, you would use a Regex (\w*) (\w*) with two grups, and replace it for $2, $1

Usually, the first group (0) references the whole match of the regex, being the other groups numbered according to the order where they are in your expression.