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Avoid the with statement

function,

sayFirstNameToo()

, can also access it. Suppose you now change this example to use

var

like this:

function sayFirstName() {

var sMyFirstName = “Nicholas”;

alert(sMyFirstName);

}

function sayFirstNameToo() {

alert(sMyFirstName);

}

sayFirstName();

sayFirstNameToo();

When you try to run this code, you get an error after the first alert is displayed because the second func-

tion has no knowledge of a variable named

sMyFirstName

. The variable was created within the

sayFirstName()

scope and was destroyed when the function finished executing.

Using local variables leads to faster execution because the interpreter doesn’t have to leave the local

scope in search of a variable. Local variables are also much more efficient because they are removed

from memory long before the Web page is unloaded.

Avoid the with statement

You probably understand at this point that the fewer scopes you have, the better off you are. This is why

it’s important to avoid the

with

statement whenever possible.

As a quick refresher, the

with

statement enables you to access properties of objects as if they were vari-

ables, so instead of doing this:

alert(document.title);

alert(document.body.tagName);

alert(document.location);

You can do this:

with (document) {

alert(title);

alert(body.tagName);

alert(location);

}

This saves bytes by eliminating the need to type

document

for each of the three lines contained in the

with

statement. But the

with

statement comes with a price: It is another scope. When you use the

with

statement, you are forcing the interpreter to not only look up the scope tree for local variables, but you

are also forcing it to test each variable against the object specified to see if it’s a property. After all, you

could have a variable named

title

location

defined within the function as well.

Your best bet is to avoid using the

with

statement. The number of bytes saved doesn’t outweigh the per-

formance loss because of an added scope.

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