Regular Expressions and Pattern Matching - JavaScript by Example - page 721

17.2.3 Testing the Expression

The RegExp object has two methods that can be used to test for a match in a string,
the test() method and the exec() method, which are quite similar. The test() method
searches for a regular expression in a string and returns true if it matched and false if
it didn't. The exec() method also searches for a regular expression in a string. If the
exec() method succeeds, it returns an array of information including the search string,
and the parts of the string that matched. If it fails, it returns null . This is similar to the
match() method of the String object. Table 17.2 summarizes the methods of the Reg-
Exp object.

Table 17.2 Methods of the RegExp Object

Method What It Does

exec Executes a search for a match in a string and returns an array.

test Tests for a match in a string and returns either true or false.

The test() Method. The RegExp object's test() method is used to see if a string con-
tains the pattern represented in the regular expression. It returns a true or false Bool-
ean value. After the search, the lastIndex property of the RegExp object contains the
position in the string where the next search would start. (A string starts at character
position 0.) If a global search is done, then the lastIndex property contains the starting
position after the last pattern was matched. (See Example 17.4 to see how the lastIndex
property is used.)
Steps to test for a match:

1. Assign a regular expression to a variable.
2. Use the regular expression test() method to see if there is a match. If there is a
match, the test() method returns true ; otherwise, it returns false . There are also
four string methods that can be used with regular expressions. (See section
“String Methods Using Regular Expressions” on page 727.)

FORMAT

var string="String to be tested goes here";
var regex = /regular expression/; // Literal way

var regex =new RegExp("regular expression"); // Constructor way

regex.test (string); // Returns either true or false

or

/regular expression/.test("string");