If you specifically want to match words then try something like this:

/in[a-z]*ing/i

If you want in followed by any characters at all followed by ing then:

/in.*ing/i

The i after the second / makes it case insensitive. Either way replace the * with + if you want to have at least one character in between in and ing; * matches zero or more.

Given a variable in a string you could use the regex to test for a match like this:

var str = Interesting;

if (/in[a-z]*ing/i.test(str)) {

    // we have a match

}

UPDATE

What if the prefix and suffix are stored in variables?

Well then instead of using a regex literal as shown above you'd use new RegExp() and pass a string representing the pattern.

var prefix = in,

    suffix = ing,

    re = new RegExp(prefix + [a-z]* + suffix, i);

if (re.match(Interesting)) {

    // we have a match

}

All of the regular expressions I've shown so far will match the in something ing pattern anywhere within a larger string. If the idea is to test whether the entire string matches that mattern such that interesting would be a match but noninterestingstuff would not (as per stackunderflow's comment) then you need to match the start and end of the string with ^ and $:

/^in[a-z]*ing$/i

Or from variables:

new RegExp(^ + p + [a-z]* + s + $, i)

Or if you're testing the whole string you don't necessarily need regex (although I find regex simpler):

var str = Interesting,

    prefix = in,

    suffix = ing;

str = str.toLowerCase(); // if case is not important



if (str.indexOf(prefix)===0 && str.endsWith(suffix)){

   // match do something

}

Or for browsers that don't support .endsWith():

if (str.slice(0,prefix.length)===prefix && str.slice(-suffix.length)===suffix)

What's the best I can read on the subject?

MDN gives a rundown of regex for JavaScript. regular-expressions.info gives a more general set of tutorials.