Many IDE's provide a function to find and replace across files in your project, of course VIM can do this too by using the "arg" commands, without switching to the terminal!

There are 2 steps to the task, first we provide a set of files for the replacement to happen on. The second part is telling VIM what to replace. Take a look at this example:

:args javascript/*
:argdo %s/foo/bar/g | update

Running these 2 commands in VIM will loop through all files in the "javascript" folder and replace all instances of "foo" with "bar".

Of course this is a contrived example, you will likely want to specify which files are used and you may not want to replace every instance of your search, so additional options can be added.

:args javascript/**/*.js
:argdo %s/foo/bar/gc | update

Notice that you can use the unix "glob" pattern to specify the file locations. Additionally, adding the "c" flag to your regex will inform VIM to ask for a yes/no response on every match before replacing.

For help learning regex, take a look at the following sites:

Regular Expressions (Information and tutorials)
Learn Regex The Hard Way (Online book)
Regexpal (Online expression tester)