title: What does it mean to 'wrap' a function?
body: <p>I've been running across this idea and struggle to understand its meaning.</p>
  <p>This is one example:</p>
  <p>'In terms of what they can express, callbacks and promises are equivalent. Callback-based functions can be wrapped to expose a promise-based interface, and vice versa.'</p>
  <p>I'm less interested in the context of this example, than I am in what it means to 'wrap a function'.</p>