Regex basics in Javascript.md

What's regex?

Define a search pattern that can be used to search for things in a string.

Some regex symbols to match patterns

• .test( . . . ) : returns true or false
• match( . . . ) : returns the match
• /patternToLookFor/ig: i and g at the end are flags meaning can insensitiveness and every occurrence, respectively.
• . : match anything with a wildcard period
• [ ]: match single characters with multiple possibilities
• [a-z]: match all lowercased letters of the alphabet
• [^0-9]/ig: the ^inside brackets matches singles characters not specified. For example, this won't match any number in the entire string, no matter the case.
• +: one or more times
• *: zero or more times
• ^word: matches word at the beginning of the string. Notice it's without the brackets []
• word$: the $ matches the case at the end of the string
• \w : every letter and number
• \W: every non letter and number
• \d: all numbers
• \D: all non numbers
• \s: all whitespaces
• \S: all non whitespaces
• { , }: curly brackets for quantity identifiers. It can be inserted a lower bound number and/or upper bound number of characters, or even only one number telling the exact number of characters

Some examples

1. Using regex to check if a username matches the following requirements:

• if there are numbers, they MUST be at the end
• letters can be lowercase and uppercase
• at least two characters long. Two-letter names can't have numbers A possible pattern would be: /^[A-Za-z]{2,}\d*$/

2. Using capture groups (written inside parentheses) and the replace method to invert the order of a word:

• "Code Camp".replace(/(\w+)\s(\w+)/, '$2 $1') returns "Camp Code"