javascript

Chapter 5: Reference Types
matches = pattern2.exec(text);
alert(matches.index); //5
alert(matches[0]);
//bat
alert(pattern2.lastIndex); //8
The first pattern in this example, pattern1 , is not global, so each call to exec() returns the first match
only ( “ cat “ ). The second pattern, pattern2 , is global, so each call to exec() returns the next match in
the string until the end of the string has been reached. Note also how the pattern ’ s lastIndex property
is affected. In global matching mode, lastIndex is incremented after each call to exec() , but it remains
unchanged in nonglobal mode.
A deviation in the IE implementation of JavaScript causes lastIndex to always be
updated, even in nonglobal mode.
Another method of regular expressions is test() , which accepts a string argument and returns true if
the pattern matches the argument, and false if it does not. This method is useful when you want to
know if a pattern is matched but you have no need for the actual matched text. The test() method is
often used in if statements, such as the following:
var text = “000-00-0000”;
var pattern = /\d{3}\-\d{2}-\d{4}/;
if (pattern.test(text)){
alert(“The pattern was matched.”);
}
In this example, the regular expression tests for a specific numeric sequence. If the input text matches the
pattern, then a message is displayed. This functionality is often used for validating user input, when you
care only if the input is valid, not necessarily why it ’ s invalid.
The inherited methods of toLocaleString() and toString() each return the literal representation of
the regular expression, regardless of how it was created. Consider this example:
var pattern = new RegExp(“\\[bc\\]at”, “gi”);
alert(pattern.toString());
// /\[bc\]at/gi
alert(pattern.toLocaleString()); // /\[bc\]at/gi
Even though the pattern in this example is created using the RegExp constructor, the
toLocaleString() and toString() methods return the pattern as if it were specified in literal format.
The valueOf() method for a regular expression returns the regular expression itself.
This oddity occurs partially because the specification does not indicate what value
should be returned by this method.
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