title: Why most of the Number prototype functions has a global duplicate function?
body: <p>I really wonder, what is the purpose of having 2 duplicate functions.</p>
  <p>For example:</p>
  <blockquote>
  <p>isFinite() and Number.isFinite()</p>
  <p>isNaN() and Number.isNaN()</p>
  </blockquote>
  <p>But for example there is no <code>IsInteger()</code> function, when there is <code>Number.isInteger()</code>.</p>
  <p>What is the difference?</p>
  <p>Why duplicates exists?</p>
  <p>When one should use Number prototype function or the Global function?</p>