title: JS: check existence of a var that equals 0
body: <p>I have a piece of code that tests for the existence of a variable, using an if statement like the example below. I need to do one thing if the var is set, a different thing if its not. In a certain test case, the var needed to be set to 0, but that is the same is having an unset var in JS, apparently:</p>
  
  <pre><code>var toMatch;
  toMatch = 0;
  if (!toMatch) {
      document.write("no");
  } else {
      document.write(toMatch);
  }
  
  // html is "no"
  </code></pre>
  
  <p><a href="http://jsfiddle.net/u2cpu/" rel="noreferrer">jsFiddle</a></p>
  
  <p>So my problem is, how do I test for a var if its value is legitimately zero. I should point out, that in my function possible values to be passed are 0-40+.</p>
  
  <p>In the past I've used a work around like setting the initial value to a number high enough that it is not likely to be passed to the function but that seems hackey to me. Is there a better way to do it?</p>