📖 JavaScript Regular Expressions
Regular Expression Object: RegExp
Regular expressions are used to perform powerful pattern-matching and "search-and-replace" functions on text. A regular expression object describes a pattern of characters. When you search in a text, you can use a pattern to describe what you are searching for. A simple pattern can be one single character or a more complicated pattern can consist of more characters, and can be used for parsing, format checking, substitution and more.
/* validEmail validates an email address against a regular expression and returns true or false */
function validEmail(email) {
var emailRegex = /[-\w.]+@([A-z0-9][-A-z0-9]+\.)+[A-z]{2,4}/;
var valid = email.match(emailRegex);
return valid;
}| Regular Expression Flags | |
|---|---|
| i | Case Insensitive |
| g | Global (all matches) |
| Regular Expression Character Positions | |
| ^ | beginning of the text string |
| $ | end of the text string |
| \b | presence of a word boundary |
| \B | absence of a word boundary |
| Regular Expression Character Classes | |
| \d | digit (0-9) |
| \D | non-digit |
| \w | word character (a-z, A-Z, 0-9, _) |
| \W | non-word character (special characters) |
| \s | white-space character (blank space, tab, newline, carriage return, or formfeed |
| \S | non-white spce character |
| . | any character |
| [chars] | match any character in the list of characters chars |
| [^chars] | match any character not in the list of characters chars |
| [char1-charN] | match any character in the range char1 - charN |
| [^char1-charN] | match any character not in the range char1 - charN |
| [a-z] | match lowercase letters |
| [A-Z] | match uppercase letters |
| [a-zA-Z] | match letters (uppercase or lowercase) |
| [0-9] | match digits |
| Repetition Characters | |
| * | Repeat 0 or more times |
| ? | Repeat 0 or 1 time |
| + | Repeat 1 or more times |
| {n} | Repeat exactly n times |
| {n,} | Repeat at least n times |
| {n,m} | Repeat at least n times but no more than m times |
| Escape Sequences | |
| \/ | / |
| \\ | \ |
| \. | . |
| \* | * |
| \+ | + |
| \? | ? |
| \| | | |
| \(\) | () |
| \{\} | {} |
| \^ | ^ |
| \$ | $ |
| \n | new line |
| \r | carriage return |
| \t | tab |
| Regular Expression Methods | |
| string.match(re) | performs a pattern match on string against the regular expression re; returns true or false |
| string.match(re/g) | returns an array of all matched text |
| string.replace(re,'newtext') | replaces any text within the string string that matches the regular expression re with the string supplied in newtext |
| Useful Regular Expressions | |
| U.S. Zip Code | \d{5}(-\d{4})? |
| U.S. Phone Number | \(?(\d{3})\)?[ -.](\d{3})[ -.](\d{4}) |
| Email address | [-\w.]+@([A-z0-9][-A-z0-9]+\.)+[A-z]{2,4} |
| Date | ([01]?\d)[-\/ .]([123]?\d)[-\/ .](\d{4}) |
| Web address | ((\bhttps?:\/\/)|(\bwww\.))\S* |