A hash, also known as an associative array, is a collection of data in which each piece of data has two components: a key and a value. Much like the hash at your local diner, JavaScript hashes go unordered: They’re not indexed by numbers. For example, if you wish to use JavaScript to put up a different GIF animation on your site every day of the week, you might throw all these animations into a hash associated to each weekday as a key. Then you would refer to the key day to invoke that day’s animation.

For example, in a normal array, you’d have:

  dinner[0] = "monkey brain";

  dinner[1] = "meatloaf";

But in a hash, you could use a string as the index:

  dinner["monday"] = "monkey brain";

  dinner["tuesday"] = "meatloaf";

A loop is like a programming thought. Say you’re a police officer using a radar gun to catch speeding motorists. If the speed limit is 55 miles per hour, you might say to yourself: “If a car makes my radar gun display a higher value than 55, I’ll pull them over, but until then I will continue to take readings. And perhaps snack on this cruller.” In programming, the statement of this loop would be the action (firing up your motorcycle and chasing the speeder), and the expression would be the evaluation of whether or not the passing car made your radar gun read higher than 55. This is an example of a “while” loop:

  while (carSpeed < 55) {

  carSpeed = readRadar();

  // note:readRadar() should return the latest carSpeed

}



pullEmOver();  // this will only execute once carSpeed is >= 55