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Regex

JavaScript Regex​

  • A quick and easy way to test a string against a regular expression is with the test() method.
  • The test() method returns a boolean value.
  • Here is the format:
// Simple
const string = `The fat cat ran down the street. It was searching for a mouse to eat.`
console.log(/e/g.test(string)) // true

// RegExp object
const regex01 = new RegExp(/e/, 'g');
console.log(regex01.test(string))

Learn Regular Expressions In 20 Minutes​

Video: https://www.youtube.com/watch?v=rhzKDrUiJVk

  • The string used: The fat cat ran down the street. It was searching for a mouse to eat.
  • The basic format of a regex is:
    • /pattern/flags
    • / is the start of the regex
    • / is the end of the regex
    • the pattern is the part that will be matched
    • the flags are the options that will be used when matching like g for global, i for case insensitive, etc.
      • the flags are optional
  • Flags:
    • g: global - is like "match all" whereas without this flag, it will only match the first match
    • i: ignore case - will ignore the case of the characters
  • The special characters in regex is where it gets more powerful.
  • +: one or more
    • /e+/ will match e one or more times: so e will match with the and street. Without the +, the two e's in "street" would be two separate matches
  • ?: zero or one
    • it makes the character before it "optional". so /ea? will match with "the", "street", and "mouse" because they have an "e" but it will also match with "eat"
  • *: zero or more
    • like the ? operator, but it will match zero or more times. So /ea* will match with "searching" but would also match with "eaa" or "eaaaa".
    • /re* matches with anything that has an "r" but also will match "street"
  • .: any character
    • /.at/ will match "fat", "cat", and "eat"
  • \w: word character
    • letters
  • \W: non-word character
    • \W will match with anything that is not a letter
  • \s: whitespace character
    • \s will match with spaces, tabs, newlines, etc.
  • \S: non-whitespace character
  • \w{4,5}: word character with a length of 4 or 5
    • you'll notice that a long word like "searching" matches on "searc" and "hing" (on the Regex site)
    • If you wanted only 4-5 character words, I think you'd need to add more specifiers
  • /[fc]at/: match with "fat" or "cat"
    • /[fc]at/ will match with "fat" and "cat" but not "eat"
  • (): capture grouping
  • ^: beginning of string
  • $: end of string