Main Page

Remember Computer Science 101

Remember Computer Science 101
A lot of the basics relating to optimization of code in other programming languages also apply to
JavaScript. Because JavaScript borrows syntax and statements so heavily from C, Java, and Perl, the
same techniques used to optimize code in those languages can also be used in JavaScript. The techniques
presented in this section have been written about in books and articles such as Koushik Ghosh’s
“Writing Efficient C and C Code Optimization” (available online at
). In this article, Ghosh has compiled a list of the most popular code
optimization techniques for C, many of which apply to JavaScript as well.
Choosing the right algorithm
When programming, choosing the right algorithm is as important as anything you do. The less complex
the algorithm, the faster your code runs. To measure the complexity of algorithms, computer scientists
use Big O notation. Big O notation consists of the letter
defined as a function with certain arguments.
The simplest algorithm is a constant value, represented as O(1). Retrieving a constant value is an extremely
fast process. Constant values are made up of both true constants, such as the number 5, as well as values
stored in variables. Consider the following example:
var iFive = 5;
var iSum = 10 + iFive;
This code retrieves three constant values. The first two are the number 10 and the variable
in the
second line. Then, in Line 3, the value of
is retrieved; this is also a constant value. These three con-
stant retrievals take very little time because of their simplicity.
All values stored in arrays are also constant values, so the following code uses only the constant value
var aNumbers = [5,10];
var iSum = aNumbers[0] + aNumbers[1];
In this code the array
is used to store the numbers to be added. Both
are constant value retrievals, so the total number of O(1) algorithms in this code is
also three.
The next algorithm is called linear, represented by O(
). This algorithm is used in simple searches, where
an array is searched through, item by item, until a result is found. The following is an example of a lin-
ear algorithm:
for (var i=0; i < aNumbers.length; i++) {
if (aNumbers[i] == 5) {
alert(“Found 5”);
Chapter 19
22_579088 ch19.qxd 3/28/05 11:43 AM Page 582

JavaScript EditorFree JavaScript Editor     Ajax Editor