Defining RegExp in JavaScriptIntroduction
The RegExp object is used to store the search pattern.
We define a RegExp object with the new keyword. The following code line defines a RegExp object called patt1 with the pattern "e": <pre name="code" class="brush:c-sharp"> var patt1=new RegExp("e"); </pre> When you use this RegExp object to search in a string, you will find the letter "e".
Methods of the RegExp Object
The RegExp Object has 3 methods: test(), exec(), and compile().
test() method
The test() method searches a string for a specified value. Returns true or false
Example
<pre name="code" class="brush:c-sharp"> var patt1=new RegExp("e") document.write(patt1.test("The best things in life are free"));
Since there is an "e" in the string, the output of the code above will be:
true
exec() Method
The exec() method searches a string for a specified value. Returns the text of the found value. If no match is found, it returns null
Example 1
<pre name="code" class="brush:c-sharp">var patt1=new RegExp("e"); document.write(patt1.exec("The best things in life are free")); Since there is an "e" in the string, the output of the code above will be:
e
You can add a second parameter to the RegExp object, to specify your search. For example; if you want to find all occurrences of a character, you can use the "g" parameter ("global").
When using the "g" parameter, the exec() method works like this:
• Finds the first occurence of "e", and stores its position
• If you run exec() again, it starts at the stored position, and finds the next occurence of "e", and stores its position
Example 2
<pre name="code" class="brush:c-sharp"> var patt1=new RegExp("e","g");
do
{
result=patt1.exec("The best things in life are free");
document.write(result);
} while (result!=null)
Since there is six "e" letters in the string, the output of the code above will be:
eeeeeenull
compile() Method
The compile() method is used to change the RegExp.
compile() can change both the search pattern, and add or remove the second parameter.
Example
<pre name="code" class="brush:c-sharp">
var patt1=new RegExp("e");
document.write(patt1.test("The best things in life are free"));
patt1.compile("d");
document.write(patt1.test("The best things in life are free"));
Since there is an "e" in the string, but not a "d", the output of the code above will be:
truefalse