A regular expression is a pattern of characters. The pattern is used to do pattern-matching “search-and-replace” functions on text.

Method:

1. test: The test() method tests for a match in a string. If it finds a match, it returns true, otherwise it returns false.

var text = "The best things in life are free"; 
var pattern = /e/;
var result = pattern.test(text);

2. exec or match: The exec() method tests for a match in a string. If it finds a match, it returns a result array, otherwise, it returns null.

var text = "The best things in life are free";
var pattern = /e/;
var result = text.match(pattern);

3. Replace: To replace pattern in characters, use replace() – Replace special characters

var values = '&677,431,444,98777';
var result=values.replace(/({[@!#$%*_^\&]})|,/g, '');
console.log(result);

Pattern Designing & Pattern Concept:

Simple Pattern :

• [abc] – a,b or c
• [^abc] – Any character except a,b or c
• [a-z] – a to z
• [A-Z] – A to Z
• [a-z A-Z] – a to z or A-Z
• [0-9] – 0-9 digit

Meta Characters:

• \d – Digit [0-9]
• \D – Not a digit [^0-9]
• \w – Word Charecter [a-z A-Z 0-9 _)
• \W – Not a Word charecter
• \s – White space (space, tab, newline)
• \S – Not Whitespace
• ^ – Beginning of string
• $ – End of string
• () – Group
• | – Either or

Quantifiers:

• [ ]? – Occurs 0 or 1 Times
• [ ]+ – Occurs 1 or More times
• [ ]* – Occurs 0 or More times
• [ ]{n} – Occurs n or more times
• [ ]{y,z} – Occurs Starts with y & Ends with z

Testing Tools

https://regex101.com/

Question & Answer:

1. Accept only numbers in string fields?
2. Accept only Characters in string fields?
3. Check whether strings have a special character or not.
4. Fields should only accept email addresses.
5. Replace all special character