title: TypeScript and array reduce function
body: <p>Do you know what the <code>reduce</code> array method does in TypeScript?
  Can you provide a simple example of usage?</p>
  <p>I searched on Google and the <a href="http://www.typescriptlang.org/Content/TypeScript%20Language%20Specification.pdf" rel="noreferrer">TypeScript language specification</a> but could not find any decent explanation and examples.</p>