When a web project starts getting big, managing dependencies becomes hard if you don’t have the right tools. If you have some experience with web development, you probably use RequireJS to manage your dependencies.
RequireJS does a great job but if you are familiar with node, you probably wish it was as easy in the browser. Dependency management is built into node, so you don’t have to worry about it.
Browserify lets you write node-style code that works in the browser. It is basically a replacement for RequireJS that allows you to create bundles with less configuration.