title: how to declare an empty numeric (number) value in javaScript
body: <p>I need to create an object with some non-defined values.
  I know how to declare an empty string- in example that would be a object.name. But what would be an empty numeric value. What do I need to put instead of word 'number' in object.age property to tell the javaScript it should be any number? </p>
  
  <pre><code>let object = {
  name : ''
  age : number
  }
  </code></pre>