Beginning JavaScript with DOM Scripting and Ajax, 2nd Edition

Chapter 2 ■ Data and Decisions
Let’s do that next, using the prompt()method to obtain the user’s e-mail address and then check the input for the
@ symbol, returning the index of the symbol using indexOf():
var userEmail= prompt("Please enter your emailaddress ", "" );
document.write( userEmail.indexOf( "@" ) );
If the @ is not found, –1 is written to the page. As long as the character is there in the string somewhere, its
position in the index—in other words, something greater than –1,will be returned.
The substring() method carves one string from another string, taking the indexes of the start and end positions
of the substring as parameters. You can return everything from the first index to the end of the string by leaving off the
second parameter.
So, to extract all the characters from the third character (at index 2) to the sixth character (index 5), you’d write
var myOldString = "Hello World";
var myNewString = myOldString.substring( 2, 5 );
document.write( myNewString );
You should see llo written out to the browser. Note that the substring() method copies the substring that it
returns, and it doesn’t alter the original string.
The substring() method really comes into its own when you’re working with unknown values. Here’s another
example that uses both the indexOf() and substring() methods:
var characterName = "my name is Simpson, Homer";
var firstNameIndex = characterName.indexOf( "Simpson," ) + 9;
var firstName = characterName.substring( firstNameIndex );
document.write( firstName );
You’re extracting Homer from the string in the variable characterName, using indexOf() to find the start of the last
name and adding 9 to it to get the index of the start of the first name (because "Simpson, " is 9 characters long), and
storing it in firstNameIndex. This is used by the substring() method to extract everything from the start of the first
name—you haven’t specified the final index, so the rest of the characters in the string will be returned.
Now let’s look at the Date object. This allows you to store dates and provides some useful date/time-related
functionality.
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