- **Epistemic status:** #seedlings
#### Testing a regex
Use the `.test()` method
```javascript
const testString = "My test string";
const testRegex = /string/;
testRegex.test(testString);
```
#### Testing Multiple Patterns
Use the OR operator `(a|b)`
```javascript
const regex = /yes|no|maybe/;
```
#### Ignoring case
Use the `i` flag for case insensitivity
```javascript
const caseInsensitiveRegex = /ignore case/i;
const testString = 'We use the i flag to iGnOrE CasE';
caseInsensitiveRegex.test(testString); // true
```
#### Extracting First Match To A Variable
Use the `.match()` function
```javascript
const match = "Hello World!".match(/hello/i); // "Hello"
```
#### Extracting All The Matches In An Array
Use the `g` flag
```javascript
const testString = "Repeat repeat rePeAT";
const regexWithAllMatches = /Repeat/gi;
testString.match(regexWithAllMatches); // ["Repeat", "repeat", "rePeAT"]
```
#### Matching Any Character
Use the wildcard character `.` to be a placeholder for any character.
```javascript
// To match "cat", "BAT", "fAT", "mat"
const regexWithWildcard = /.at/gi;
const testString = "cat BAT cupcake fAT mat dog";
const allMatchingWords = testString.match(regexWithWildcard); // ["cat", "BAT", "fAT", "mat"]
```
#### Matching A Single Character With Multiple Possibilities
Use character classes, which allow you to define a group of characters you wish to match. You place them inside square brackets `[]`
```javascript
// Match "cat" "fat" and "mat" but not "bat"
const regexWithCharClass = /[cfm]at/g;
const testString = "cat fat bat mat";
const allMatchingWords = testString.match(regexWithCharClass); // ["cat", "fat", "mat"]
```
#### Match Letters Of The Alphabet
Use a range within the character set `[a-z]`
```javascript
const regexWithCharRange = /[a-e]at/;
const catString = "cat";
const batString = "bat";
const fatString = "fat";
regexWithCharRange.test(catString); // true
regexWithCharRange.test(batString); // true
regexWithCharRange.test(fatString); // false
```
#### Match Specific Numbers and Letters
You can also use the hyphen to match numbers
```javascript
const regexWithLetterAndNumberRange = /[a-z0-9]/ig;
const testString = "Emma19382";
testString.match(regexWithLetterAndNumberRange) // true
```
#### Match A Single, Unknown Character
To match a set of characters you don't want to have, use the negated character set. To negate a character set, use a caret `^`
```javascript
const allCharsNotVowels = /[^aeiou]/gi;
const allCharsNotVowelsOrNumbers = /[^aeiou0-9]/gi;
```
#### Match Characters That Occur One Or More Times In A Row
Use the `+` symbol
```javascript
const oneOrMoreAsRegex = /a+/gi;
const oneOrMoreSsRegex = /s+/gi;
const cityInFlorida = "Tallahassee";
cityInFlorida.match(oneOrMoreAsRegex); // ['a', 'a', 'a'];
cityInFlorida.match(oneOrMoreSsRegex); // ['ss'];
```
#### Matches characters that occur zero or more times in a row
Use the asterisk `*`
```javascript
const zeroOrMoreOsRegex = /hi*/gi;
const normalHi = "hi";
const happyHi = "hiiiiii";
const twoHis = "hiihii";
const bye = "bye";
normalHi.match(zeroOrMoreOsRegex); // ["hi"]
happyHi.match(zeroOrMoreOsRegex); // ["hiiiiii"]
twoHis.match(zeroOrMoreOsRegex); // ["hii", "hii"]
bye.match(zeroOrMoreOsRegex); // null
```
#### Lazy Matching
The smallest part of a string that matches the given requirements. Regex, by default, are greedy (matches the longest portion of a string meeting the given requirements). Use the `?` character to lazy match
```javascript
const testString = "catastrophe";
const greedyRexex = /c[a-z]*t/gi;
const lazyRegex = /c[a-z]*?t/gi;
testString.match(greedyRexex); // ["catast"]
testString.match(lazyRegex); // ["cat"]
```
#### Match starting string patterns
To test for a match of characters at the beginning of a string, use the caret `^`, but outside of the character set
```javascript
const emmaAtFrontOfString = "Emma likes cats a lot.";
const emmaNotAtFrontOfString = "The cats Emma likes are fluffy.";
const startingStringRegex = /^Emma/;
startingStringRegex.test(emmaAtFrontOfString); // true
startingStringRegex.test(emmaNotAtFrontOfString); // false
```
#### Match ending string patterns
Use the dollar sign `
at the end of a regex to check whether a pattern exists at the end of a string
```
const emmaAtBackOfString = "The cats do not like Emma";
const emmaNotAtBackOfString = "Emma loves the cats";
const startingStringRegex = /Emma$/;
startingStringRegex.test(emmaAtBackOfString); // true
startingStringRegex.test(emmaNotAtBackOfString); // false
```
#### Matching all letters and numbers
Use the `\word` shorthand
```javascript
const longHand = /[A-Za-z0-9_]+/;
const shortHand = /\w+/;
const numbers = "42";
const myFavoriteColor = "magenta";
longHand.test(numbers); // true
shortHand.test(numbers); // true
longHand.test(myFavoriteColor); // true
shortHand.test(myFavoriteColor); // true
```
#### Match everything except letters & numbers
You can use for the opposite of `\w` with \W
```javascript
const noAlphaNumericCharRegex = /\W/gi;
const weirdCharacters = "!_$!!";
const alphaNumericCharacters = "ab283AD";
noAlphaNumericCharRegex.test(weirdCharacters); // true
noAlphaNumericCharRegex.test(alphaNumericCharacters); // false
```
#### Match all numbers
You can use a character set `[0-9]`, or use the shorthand `\d`
```javascript
const digitsRegex = /\d/g;
const stringWithDigits = "My cat eats $20.00 worth of food a week.";
stringWithDigits.match(digitsRegex); // ["2", "0", "0", "0"]
```
#### Match all non-numbers
You can use the opposite of `\d` with `\D`
```javascript
const nonDigitsRegex = /\D/g;
const stringWithLetters = "101 degrees";
stringWithLetters.match(nonDigitsRegex); // [" ", "d", "e", "g", "r", "e", "e", "s"]
```
#### Matching whitespace
Use `\s` to match white space and carriage returns
```javascript
const sentenceWithWhitespace = "I like cats!"
const spaceRegex = /\s/g;
whiteSpace.match(sentenceWithWhitespace); // [" ", " "]
```
#### Matching non-whitespace
You can use the opposite of `\s` with `\S`
```javascript
const sentenceWithWhitespace = "C a t"
const nonWhiteSpaceRegex = /\S/g;
sentenceWithWhitespace.match(nonWhiteSpaceRegex); // ["C", "a", "t"]
```
#### Matching character counts
You can specify a specific number of characters in a row using `{lowerBound, upperBound}`
```javascript
const regularHi = "hi";
const mediocreHi = "hiii";
const superExcitedHey = "heeeeyyyyy!!!";
const excitedRegex = /hi{1,4}/;
excitedRegex.test(regularHi); // true
excitedRegex.test(mediocreHi); // true
excitedRegex.test(superExcitedHey); //false
```
#### Matching lowest number of character counts
You can define only a minimum number of character requirements with `{lowerBound,}`. This is called a quantity specifier.
```javascript
const regularHi = "hi";
const mediocreHi = "hiii";
const superExcitedHey = "heeeeyyyyy!!!";
const excitedRegex = /hi{2,}/;
excitedRegex.test(regularHi); // false
excitedRegex.test(mediocreHi); // true
excitedRegex.test(superExcitedHey); //false
```
## Matching an exact number of character counts
You can specify the exact number of character requirements with `{requiredCount}`
```javascript
const regularHi = "hi";
const bestHi = "hii";
const mediocreHi = "hiii";
const excitedRegex = /hi{2}/;
excitedRegex.test(regularHi); // false
excitedRegex.test(bestHi); // true
excitedRegex.test(mediocreHi); //false
```
## Matching all or none of a character
To check whether a character exists, use the `?`
```javascript
const britishSpelling = "colour";
const americanSpelling = "Color";
const languageRegex = /colou?r/i;
languageRegex.test(britishSpelling); // true
languageRegex.test(americanSpelling); // true
```