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This algorithm is fairly common because iterating over the values in an array is a very common tech-

nique. However, another linear algorithm is used commonly in JavaScript: the

named property lookup

Named properties are just basic properties of objects, such as

oDog.name

. Although this may look like

a variable that is local to the given object, in reality, it’s actually a search through the properties of the

object looking for the one matching

name

. For this reason, it’s always best to use local variables or

numerically indexed array values instead of named properties.

Consider this example:

var aValues = [1, 2, 3, 4, 5, 6, 7, 8];

function testFunc() {

for (var i=0; i < aValues.length; i++) {

alert(i + “/” + aValues.length + “=” + aValues[i]);

}

Here are the algorithms represented in this code:

i < aValues.length

— constant(O(1))

aValues.length

i < aValues.length

— linear(O(

))

alert(i + “/” + aValues.length + “=” + aValues[i]);

— constant(O(1))

aValues.length

alert(i + “/” + aValues.length + “=” + aValues[i]);

—

linear(O(

))

aValues[i]

alert(i + “/” + aValues.length + “=” + aValues[i]);

—

constant(O(1))

The linear algorithms are of particular interest here because they can easily be replaced with constant

algorithms. All the linear algorithms are run twice every time the loop runs: once when the

i <

aValues.length

test is run after each loop iteration, and once in the

alert()

call. That means the

linear algorithms are executed 16 times throughout the function execution.

The following code does the exact same thing, but uses only one linear algorithm:

var aValues = [1, 2, 3, 4, 5, 6, 7, 8];

function testFunc() {

for (var i=0, iCount=aValues.length; i < iCount; i++) {

alert(i + “/” + iCount + “=” + aValues[i]);

}

In this example, a second variable is initialized in the

for

loop,

iCount

, which is assigned the value of

aValues.length

. Then, the test after each iteration of the loop becomes a constant algorithm because

it is accessing the variables

and

iCount

instead of

aValues.length

. Likewise, by replacing

aValues.length

with

iCount

in the

alert()

call, another linear algorithm is eliminated. Ultimately,

this code executes with only one linear algorithm instead of 16, which decreases execution time.

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