JavaScript – Regular Expressions – Ameerpet Technologies

Regular Expression:

Regular expression is a set of characters called Pattern.
These Patterns are used to search required information from the given text.
JavaScript providing RegExp object with Properties and Functions.

Some of the Regular Expressions for Alphabets and Numerical Validation

[abc] – find any character in the brackets a, b or c
[a-z] – find characters a to z lowercase.
[0-9] – Find all digits

[^xyz] – find any character other than specified in the brackets.
[^abc] Find any character NOT between the brackets
[^0-9] Find any character NOT between the brackets (any non-digit)

(word) – find the “word” specified in the round brackets
[abc|xyz] – find either the characters a,b,c or x,y,z

Non-Empty Text Field validation: In the program, we are not using any regular expression. We check the length of input to specify Error message if the user not entered any value.

<html>
            <head>
                        <script>
                                    function valid(){
                                                var x = document.getElementById(‘val’).value;
                                                if(x.length == 0){
                                                            alert(“Please Enter Name”);
                                                            document.getElementById(‘val’).focus();
                                                            return false;
                                                }
                                                return true;
                                    }
                        </script>
            </head>
            <body>
                        <form>
                                    Enter Name : <input type=’text’ id=’val’/>
                                    <input type=’button’ onclick=”valid()” value=’Submit’ />
                        </form>
            </body>
</html>

Program to Validate only Numerical input:

<html>
            <head>
                        <script>
                                    function valid(){
                                                var x = document.getElementById(‘val’).value;
                                                var expr = new RegExp(“^[0-9]”);
                                                if(expr.test(x)){
                                                            alert(“Thank you for your valid input”);
                                                }
                                                else{
                                                            alert(“Please eneter numbers only”);
                                                            document.getElementById(‘val’).focus();
                                                }
                                    }
                        </script>
            </head>
            <body>
                        <form>
                                    Enter Age : <input type=’text’ id=’val’/>
                                    <input type=’button’ onclick=”valid()” value=’Submit’ />
                        </form>
            </body>
</html>

Program to Validate only Alphabetical Input:

<!doctype html>
<html>
            <head>
                        <script>
                                    function valid(){
                                                var x = document.getElementById(‘val’).value;
                                                var expr = new RegExp(“^[a-zA-Z]”);
                                                if(expr.test(x)){
                                                            alert(“Thank you for your valid input”);
                                                }
                                                else{
                                                            alert(“Name should not contain numbers”);
                                                            document.getElementById(‘val’).focus();
                                                }
                                    }
                        </script>
            </head>
            <body>
                        <form>
                                    Enter Name : <input type=’text’ id=’val’/>
                                    <input type=’button’ onclick=”valid()” value=’Submit’ />
                        </form>
            </body>
</html>

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