javascript-patterns/general-patterns/for-loops.html at master · Pythoning/javascript-patterns · GitHub

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<!doctype html>
<html lang="en">
	<head>
		<title>JavaScript Patterns</title>
		<meta charset="utf-8">
	</head>
	<body>
		<script>
			/* Title: for loops
			 * Description: optimized for loops
			 */

			// sub-optimal loop
			for (var i = 0; i < myarray.length; i++) {
				// do something with myarray[i]
			}

			// optimization 1 - cache the length of the array with the use of `max`
			for (var i = 0, max = myarray.length; i < max; i++) {
				// do something with myarray[i]
			}


			// optimization 2 - use single var pattern for consistency
			// NOTE: A drawback is that it makes it a little harder to copy and paste whole loops while refactoring code.
			var i = 0,
					max,
					myarray = [];

			for (i = 0, max = myarray.length; i < max; i++) {
				// do something with myarray[i]
			}


			// optimization 3 - substitute `i++` with `i = i + 1`  or `i += 1` to avoid excessive trickiness
			var i = 0,
					max,
					myarray = [];

			for (i = 0, max = myarray.length; i < max; i += 1) {
				// do something with myarray[i]
			}


			// preferred 1
			var i, myarray = [];
			for (i = myarray.length; i--;) {
				// do something with myarray[i]
			}


			// preferred 2
			var myarray = [],
					i = myarray.length;
			while (i--) {
				// do something with myarray[i]
			}


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