javascript - Create RegExps on the fly using string variables

Question

Say I wanted to make the following re-usable:

function replace_foo(target, replacement) {
   return target.replace("string_to_replace",replacement);
}

I might do something like this:

function replace_foo(target, string_to_replace, replacement) {
   return target.replace(string_to_replace,replacement);
}

With string literals this is easy enough. But what if I want to get a little more tricky with the regex? For example, say I want to replace everything but string_to_replace. Instinctually I would try to extend the above by doing something like:

function replace_foo(target, string_to_replace, replacement) {
   return target.replace(/^string_to_replace/,replacement);
}

This doesn't seem to work. My guess is that it thinks string_to_replace is a string literal, rather than a variable representing a string. Is it possible to create JavaScript regexes on the fly using string variables? Something like this would be great if at all possible:

function replace_foo(target, string_to_replace, replacement) {
   var regex = "/^" + string_to_replace + "/";
   return target.replace(regex,replacement);
}

Answer 1

There's new RegExp(string, flags) where flags are g or i. So

'GODzilla'.replace( new RegExp('god', 'i'), '' )

evaluates to

zilla