> let sentence = 'This is a sample string'

> /is/.test(sentence)
< true
> /xyz/.test(sentence)
< false

> if (/ring/.test(sentence)) {
      console.log('mission success')
  }
< mission success

> new RegExp('dog', 'i')
< /dog/i

> new RegExp('123\\tabc')
< /123\tabc/

> let greeting = 'hi'
> new RegExp(`${greeting.toUpperCase()} there`)
< /HI there/

// string anchors
> /^cat/.test('cater')
< true
> ['surrender', 'newer', 'door'].filter(w => /er$/.test(w))
< ["surrender", "newer"]

// use 'm' flag to change string anchors to line anchors
> /^par$/m.test('spare\npar\nera\ndare')
< true

// escape metacharacters to match them literally
> /b\^2/.test('a^2 + b^2 - C*3')
< true

> let items = 'catapults\nconcatenate\ncat'
> console.log(items.replace(/^/gm, '* '))
< * catapults
  * concatenate
  * cat

> let sample = 'par spar apparent spare part'
// replace 'par' only at the start of word
> sample.replace(/\bpar/g, 'X')
< "X spar apparent spare Xt"
// replace 'par' at the end of word but not whole word 'par'
> sample.replace(/\Bpar\b/g, 'X')
< "par sX apparent spare part"

// replace either 'cat' at start of string or 'cat' at end of word
> 'catapults concatenate cat scat'.replace(/^cat|cat\b/g, 'X')
< "Xapults concatenate X sX"

// same as: /\bpark\b|\bpart\b/g
> 'park parked part party'.replace(/\bpar(k|t)\b/g, 'X')
< "X parked X party"

> function escapeRegExp(string) {
    return string.replace(/[.*+\-?^${}()|[\]\\]/g, '\\$&')
  }

> function unionRegExp(arr) {
    return arr.map(w => escapeRegExp(w)).join('|')
  }

> new RegExp(unionRegExp(['c^t', 'dog$', 'f|x']), 'g')
< /c\^t|dog\$|f\|x/g

// matches character '2', any character and then character '3'
> '42\t33'.replace(/2.3/, '8')
< "483"
// 's' flag will allow line separators to be matched as well
> 'Hi there\nHave a Nice Day'.replace(/the.*ice/s, 'X')
< "Hi X Day"

// same as: /part|parrot|parent/g
> 'par part parrot parent'.replace(/par(en|ro)?t/g, 'X')
< "par X X X"

> ['abc', 'ac', 'abbc', 'xabbbcz'].filter(w => /ab{1,4}c/.test(w))
< ["abc", "abbc", "xabbbcz"]

// entire matched portion
> 'abc ac adc abbbc'.match(/a(.*)d(.*a)/)[0]
< "abc ac adc a"
// matched portion of 2nd capture group
> 'abc ac adc abbbc'.match(/a(.*)d(.*a)/)[2]
< "c a"
// get location of matching portion
> 'cat and dog'.match(/dog/).index
< 8

// get all matching portions with 'g' flag
// no properties or group portions
> 'par spar apparent spare part'.match(/\bs?par[et]\b/g)
< ["spare", "part"]

// useful for debugging purposes as well before using 'replace'
> 'that is quite a fabricated tale'.match(/t.*?a/g)
< ["tha", "t is quite a", "ted ta"]

// same as: match(/ab*c/g)
> Array.from('abc ac adc abbbc'.matchAll(/ab*c/g), m => m[0])
< ["abc", "ac", "abbbc"]
// get index for each match
> Array.from('abc ac adc abbbc'.matchAll(/ab*c/g), m => m.index)
< [0, 4, 11]

// get only capture group portions as an array for each match
> let s = 'xx:yyy x: x:yy :y'
> Array.from(s.matchAll(/(x*):(y*)/g), m => m.slice(1))
< (4) [Array(2), Array(2), Array(2), Array(2)]
  0: (2) ["xx", "yyy"]
  1: (2) ["x", ""]
  2: (2) ["x", "yy"]
  3: (2) ["", "y"]
  length: 4
  __proto__: Array(0)

> function titleCase(m, g1, g2) {
        return g1.toUpperCase() + g2.toLowerCase()
  }
> 'aBc ac ADC aBbBC'.replace(/(a)(.*?c)/ig, titleCase)
< "Abc Ac Adc Abbbc"

> '1 42 317'.replace(/\d+/g, m => m*2)
< "2 84 634"

> let swap = { 'cat': 'tiger', 'tiger': 'cat' }
> 'cat tiger dog tiger cat'.replace(/cat|tiger/g, k => swap[k])
< "tiger cat dog cat tiger"

// split based on one or more digit characters
> 'Sample123string42with777numbers'.split(/\d+/)
< ["Sample", "string", "with", "numbers"]
// include the portion that caused the split as well
> 'Sample123string42with777numbers'.split(/(\d+)/)
< ["Sample", "123", "string", "42", "with", "777", "numbers"]

// split based on digit or whitespace characters
> '**1\f2\n3star\t7 77\r**'.split(/[\d\s]+/)
< ["**", "star", "**"]

// use non-capturing group if capturing is not needed
> '123handed42handy777handful500'.split(/hand(?:y|ful)?/)
< ["123", "ed42", "777", "500"]

// remove consecutive duplicate words separated by space
// use \W+ instead of space to cover cases like 'a;a<-;a'
> 'aa a a a 42 f_1 f_1 f_13.14'.replace(/\b(\w+)( \1)+\b/g, '$1')
< "aa a 42 f_1 f_13.14"

// add something around the entire matched portion
> '52 apples and 31 mangoes'.replace(/\d+/g, '($&)')
< "(52) apples and (31) mangoes"

// duplicate first field and add it as last field
> 'fork,42,nice,3.14'.replace(/,.+/, '$&,$`')
< "fork,42,nice,3.14,fork"

// use non-capturing groups when backreferencing isn't needed
> '1,2,3,4,5,6,7'.replace(/^((?:[^,]+,){3})([^,]+)/, '$1($2)')
< "1,2,3,(4),5,6,7"

// named capture groups, same as: replace(/(\w+),(\w+)/g, '$2,$1')
> 'good,bad 42,24'.replace(/(?<fw>\w+),(?<sw>\w+)/g, '$<sw>,$<fw>')
< "bad,good 24,42"

// change 'foo' only if it is not followed by a digit character
// note that end of string satisfies the given assertion
// note that 'foofoo' has two matches
> 'hey food! foo42 foot5 foofoo'.replace(/foo(?!\d)/g, 'baz')
< "hey bazd! foo42 bazt5 bazbaz"

// change whole word only if it is not preceded by : or --
> ':cart apple --rest ;tea'.replace(/(?<!:|--)\b\w+/g, 'X')
< ":cart X --rest ;X"

// extract digits only if it is preceded by - and followed by , or ;
> '42 foo-5, baz3; x83, y-20; f12'.match(/(?<=-)\d+(?=[;,])/g)
< ["5", "20"]

// words containing all vowels in any order
> let words = ['sequoia', 'questionable', 'exhibit', 'equation']
> words.filter(w => /(?=.*a)(?=.*e)(?=.*i)(?=.*o).*u/.test(w))
< ["sequoia", "questionable", "equation"]

// replace only 3rd occurrence of 'cat'
> 'cat scatter cater scat'.replace(/(?<=(cat.*?){2})cat/, 'X')
< "cat scatter Xer scat"

// match if 'do' is not there between 'at' and 'par'
> /at((?!do).)*par/.test('fox,cat,dog,parrot')
< false