Sunday, April 19, 2020

A practical guide to Regular Expressions (RegExp) Properties in JavaScript



Hello guys! welcome to my new tutorial post on JavaScript. In this tutorial, i will be making use of few examples to explain the RegExp property to you. Like i always do advice, make sure to ask your questions where necessary via the comment box below. Am going to be starting with the RegExp constructor property so make sure to read through very carefully.

The RegExp constructor Property

It returns a reference to the array function that created the instance's prototype.

Syntax

Its syntax is as follows -

RegExp.constructor

Return Value

Returns the function that created this object's instance

Example

Try the following example below.

<html>
     <head>
          <title> JavaScript RegExp constructor Property</title>
     </head>

     <body>
          <script  type = "text/javascript">
               var  re =  new  RegExp("string");
               document.write("re.constructor is :  "  +  re.constructor );       
          </script>
     </body>
</html>

Output

Below is the output of the above example.

re.constructor is :  function  RegExp( )  { [native code] }

You can also read our tutorial post on: Regular Expressions in JavaScript with examples


The RegExp global Property

The global property is a read-only boolean property of RegExp objects. It specifies whether a particular regular expression performs global matching, that is to know whether it was created with "g" attribute.

Syntax

Its syntax is as follows -

RegExpObject.global

Return Value

Returns "TRUE" if the "g" modifier is set, "FALSE" otherwise.

Example

Try the following example below.

<html>
     <head>
          <title> JavaScript RegExp global Property</title>
     </head>

     <body>
          <script  type = "text/javascript">
               var  re =  new  RegExp("string");

               if  ( re.global )  {
                    document.write("Test 1  -  Global property is set" );   
               }  else  {
                    document.write("Test 1  -  Global property is not set");   
               }
               re =  new RegExp( "string" ,   "g" ); 

               if  ( re.global )  {
                    document.write("<br />Test 2  -  Global property is set");            
               }  else  { 
                    document.write("<br />Test 2  -  Global property is not set");            
               }
          </script>
     </body>
</html>

Output

Below is the output of the above example.

Test 1  -  Global property is not set 
Test 2  -  Global property is set 

The RegExp ignoreCase Property

ignoreCase property is a read-only boolean property of RegExp objects. It specifies whether a particular regular expression performs a case-insensitive matching, that is to know whether it was created with "i" attribute.

Syntax

Its syntax is as follows -

RegExpObject.ignoreCase

Return Value

Returns "TRUE" if the "i" modifier is set, "FALSE" otherwise.

Example

Try the following example below.

<html>
     <head>
          <title> JavaScript RegExp ignoreCase Property</title>
     </head>

     <body>
          <script  type = "text/javascript">
               var  re =  new  RegExp("string");

               if  ( re.ignoreCase )  {
                    document.write("Test 1  -  ignoreCase property is set" );   
               }  else  {
                    document.write("Test 1  -  ignoreCase property is not set");   
               }
               re =  new RegExp( "string" ,   "i" ); 

               if  ( re.ignoreCase )  {
                    document.write("<br />Test 2  -  ignoreCase property is set");            
               }  else  { 
                    document.write("<br />Test 2  -  ignoreCase property is not set");            
               }
          </script>
     </body>
</html>

Output

Below is the output of the above example.

Test 1  -  ignoreCase property is not set 
Test 2  -  ignoreCase property is set 

You can also read our tutorial post: JavaScript while Loop


The RegExp lastIndex Property

lastIndex is a read and write property of RegExp object. For the regular expressions with the "g" attribute set, it contains an integer that specifies the character position immidiately following the last match found by RegExp.exec() and the RegExp.test() methods. These methods use this property as the starting point for the next search they conduct.

This property allows you to call those methods repeatedly, to loop through all the matches in a string and works only if the "g" modifier is set.

This property is read and write, so you can set it at any time to specify where in the target string, the next search should be starting from. The RegEx exec() and test() automatically reset the lastIndex to 0 when they fail to find a match (or another match).

Syntax

Its syntax is as follows -

RegExpObject.lastIndex

Return Value

Returns an integer that specifies the character position immidiately following the last match.

Example

Try the following example below.

<html>
     <head>
          <title> JavaScript RegExp lastIndex Property</title>
     </head>

     <body>
          <script  type = "text/javascript">
               var  str =  "JavaScript is an interesting scripting language";
               var  re =  new RegExp( "script" ,  "g" );

               re.test( str );
               document.write("Test 1  -  Current Index:  "  +  re.lastIndex );            

               re.test( str );
               document.write("<br />Test 2  -  Current Index:  "  +  re.lastIndex );            
          </script>
     </body>
</html>

Output

Below is the output of the above example.

Test 1  -  Current Index:  10
Test 2  -  Current Index:  35

The RegExp multiline Property
The multiline is a read-only boolean property of the RegExp objects. It specifies whether or not a particular JavaScript regular expression should perform multiline matching, that is to know whether it was created with "m" attribute.

Syntax
Its syntax is as follows -

RegExpObject.multiline

Return Value
Returns "TRUE" if the "m" modifier is set, "FALSE" otherwise.

Example
Try the following example below.

<html>
     <head>
          <title> JavaScript RegExp multiline Property</title>
     </head>

     <body>
          <script  type = "text/javascript">
               var  re =  new  RegExp("string");

               if  ( re.multiline )  {
                    document.write("Test 1  -  multiline property is set" );   
               }  else  {
                    document.write("Test 1  -  multiline property is not set");   
               }
               re =  new RegExp( "string" ,   "m" ); 

               if  ( re.multiline )  {
                    document.write("<br />Test 2  -  multiline property is set");            
               }  else  { 
                    document.write("<br />Test 2  -  multiline property is not set");            
               }
          </script>
     </body>
</html>

Output
Below is the output of the above example.

Test 1  -  multiline property is not set 
Test 2  -  multiline property is set 

You can also read our tutorial post on: JavaScript For Loop


The RegExp source Property
source is a read-only string property of RegExp object. It contains the text of the RegExp pattern and this text does not include delimiting slashes used in regular expression literal, and it does not include the "g", "i", and "m" attributes.

Syntax
Its syntax is as follows -

RegExpObject.source

Return Value
Returns the text used for pattern matching.

Example
Try the following example below.

<html>
     <head>
          <title> JavaScript RegExp source Property</title>
     </head>

     <body>
          <script  type = "text/javascript">
               var  str =  "JavaScript is an interesting scripting language";
               var  re =  new RegExp( "script" ,  "g" );

               ret.test( str );
               document.write("The regular expression is:  "  +  re.source );                    
          </script>
     </body>
</html>

Output
Below is the output of the above example.

The regular expression is:  script 

Alright guys! we have come to the end of this tutorial on JavaScript RegExp properties. In my next tutorial post, i will be making use of some examples to illustrate the usage of the RegExp methods available in JavaScript.

Feel free to ask your questions where necessary and i will reply to them. Follow us on our social media platforms available in order to stay up to date with our latest tutorials.

Thanks for reading and bye for now.
Share:

0 comments:

Post a Comment

Hello dear readers! Please kindly try your best to make sure your comments comply with our comment policy guidelines. You can visit our comment policy page to view these guidelines which are clearly stated. Thank you.