title: Javascript logical "!==" operator?
body: <p>I am getting back into web development, and have been trying to go over the nuances of jscript recently. I was pouring through the source of the THREEx extension library built on top of Three.JS and noticed this function</p>
  
  <pre><code>THREEx.KeyboardState.prototype.pressed  = function(keyDesc)
  {
      var keys    = keyDesc.split("+");
      for(var i = 0; i &lt; keys.length; i++){
          var key     = keys[i];
          var pressed;
          if( THREEx.KeyboardState.MODIFIERS.indexOf( key ) !== -1 ){
              pressed = this.modifiers[key];
          }else if( Object.keys(THREEx.KeyboardState.ALIAS).indexOf( key ) != -1 ){
              pressed = this.keyCodes[ THREEx.KeyboardState.ALIAS[key] ];
          }else {
              pressed = this.keyCodes[key.toUpperCase().charCodeAt(0)];
          }
          if( !pressed)   return false;
      };
      return true;
  }
  </code></pre>
  
  <p>I am looking in particular at the line here:</p>
  
  <pre><code>if( THREEx.KeyboardState.MODIFIERS.indexOf( key ) !== -1 ){
  </code></pre>
  
  <p>I am not familiar with this !== operator. I checked w3schools and their logical operators list does not have this one included. I am not sure if this is misspelled and the browsers simply count it as != or if it has some other meaning. Also I was wondering whether this is actually a single logical operator or whether it is some kind of combination, like ! + ==?</p>