When we write a page, we often need to verify the form data such as account number, ID number, etc., and the most effective and commonly used method is to use regular expressions for verification. So what is a regular expression?

Regular expression (Regular Expression) is a pattern used to describe a set of string characteristics and is used to match a specific string. Its applications are very wide, especially in string processing. Its common applications are as follows:

Verify strings, that is, verify whether a given string or substring conforms to specified characteristics, for example, verify whether it is a legal email address, verify whether it is a legal HTTP address, etc.
Search strings to find strings that match specified characteristics from the given text, which is more flexible than searching for fixed strings.
Replace a string, that is, find a string that matches a certain characteristic and then replace it.
Extract strings, that is, extract substrings that match specified characteristics from a given string.