general-patterns/single-var-pattern.html

<!doctype html>
<html lang="en">
	<head>
		<title>JavaScript Patterns</title>
		<meta charset="utf-8">
	</head>
	<body>
		<script>
			/* Title: Single var Pattern
			 Description: use one var statement and declare multiple variables
			 */

			/* Benefits:
			 * 1. Provides a single place to look for all the local variables needed by the function
			 * 2. Prevents logical errors when a variable is used before it's defined
			 * 3. Helps you remember to declare variables and therefore minimize globals
			 * 4. Is less code (to type and to transfer over the wire)
			 */

      function func() {
        var a = 1
          , b = 2
          , sum = a + b
          , myobject = {}
          , i
          , j;

        // function body...
      }

			function updateElement() {
        var el = document.getElementById("result")
          , style = el.style;
				// do something with el and style...
			}
			
			// Preferred way 
			// Move commas BEFORE vars
			// You'll not forget to add one when adding variable to the end of list
			function func() {
				var a = 1
						, b = 2
						, sum = a + b
						, myobject = {}
						, i
						, j;

				// function body...
			}

			// References
			// http://net.tutsplus.com/tutorials/javascript-ajax/the-essentials-of-writing-high-quality-javascript/
		</script>
	</body>
</html>