ActionScript for Flash MX: The Definitive Guide, Second Edition

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Copyright © 2007 O’Reilly & Associates, Inc. All rights reserved.

Working with Strings

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101

Combining String Examination with Substring Extraction

We’ve seen how to search for characters in a string and how to extract characters

from a string. These two operations are most powerful when we put them together.

Most of the examples we’ve seen so far use literal expressions as arguments, like this:

var msg = "Welcome to my website!";

var firstWord = msg.substring(0, 7); // 0 and 7 are numeric literals

That’s a decent demonstration of the way substring() works, but it doesn’t represent

the typical real-world use of substring(). More often, we don’t know the content of

the string in advance and we must generate our arguments dynamically. For exam-

ple, instead of saying something static like, “Get me the substring from index 0 to

index 7,” we usually say something dynamic like, “Get me the substring starting

from the first character and ending at the first occurrence of a space in this string.”

This more flexible approach doesn’t require us to know the content of a string in

advance. Here we extract the first word of the variable

msg, by combining substring()

with indexOf():

var firstWord = msg.substring(0, msg.indexOf(" "));

The expression msg.indexOf(" ") evaluates to the numeric index of the first space in

msg. Our technique will work regardless of the