title: What is the phenomenon of primitive values being singletons called?
body: <p>From my understanding in JavaScript (And Ruby and Python) only a single instance of a given primitive value exist in memory at any given time. For example, If you instantiate a number, then that number is created in memory. Any other variable that reinstantiates that number, will actually be referencing the same number in memory that was already created. This can be illustrated with the following example:</p>
  
  <pre><code>var x = 5;
  var y = 5;
  Object.is(x, y);
  &gt;&gt;&gt;true
  </code></pre>
  
  <p>What is the phenomenon of primitive values being singletons called?</p>