// Let's get our hands dirty with an examples: 

const regex = /[A-Z]\w+/g; // (We ommited ' ')
// regex holds a regular expression which will match words starting with a capital letter. 

const str = `Rahul, Taylor and Susanne are coders who live in India`; 

// When we apply the regex to str, it returns all matches in a simple array! 
// console.log( str.match(regex) )
//["Rahul", "Taylor", "Susanne", "India"]

  // Let's hang with them
  let regex = /code|easy/i; 
  const str = 'this code is EaSy super easy'; 
  regex.test(str) // true; means we have a match😍

  str.match(regex) // ["code", index: 5, input..]

  // Oops! We forgot adding the g flag
  regex = /code|easy/ig;

  str.match(regex) // ["code", "EaSy", "easy"]
  // ALRIGHT!!

// CHARACTER CLASSES allow you to define a group of characters you wish to match. You put the chards in [] "car cat cam cal car".match(/ca[rt]/g); 
// returns: ['car', 'cat', 'car']

// match "bag", "big", "bug", but nit "bog" "big bag has a bug bog".match(/b[aiu]g/g); 
// ["big", "bag", "bug"]

// MAKE CHARACTER CLASSES SHORTER by using [X-Y] which will match fro letter x to letter y. Example: [a-zA-Z] will match all capital and not capital letters from a to z

"abcdefghijklmnopqr".match(/[d-j]/g); 
// ["d", "e", "f", "g", "h", "i", "j"]

//same as: 
"abcdefghijklmnopqr".match(/defghij/g); 
// ["d", "e", "f", "g", "h", "i", "j"]

// Use it with a number too: 
"1234567890".match(/4-9/g); 
//["4", "5", "6", "7, "8", "9"]

// With +
let regex = /a+/g; 
"abc".match(regex) //["a"]
"aabc".match(regex) //["aa"]
"aabac".match(regex) //["aa", "a"]
"bbc".match(regex) //null

//without +
regex = /a/g; 
"abc".match(regex) //["a"]
"aabc".match(regex) //["aa"]
"aabac".match(regex) //["aa", "a"]
"bbc".match(regex) //null

let regex = /^K/; 

regex.test("__K_K_") // false - K is not exactly at the beginning!
regex.test("K___K___") // true 

//To search for a character at the end of string use $ like so

regex = /K$/; 

regex.test("__K__K_") // false - K has to be at the end

regex.test("__K") // true

let regex = /colou?r/; // makes 'u' capital

let american = "color"; 
let british = "colour"; 

regex.test(american); // true
regex.test(british); // true
regex.test("cologr"); // false

let str = "ama baalo maaaaamal aaaaaa"; 
console.log( str.match(/a{5}/g ) ); 
//prints ["aaaaa". "aaaaa"]

//to match 'm' letter followed by 5 x 'a'
console.log( str.match( /ma{5}/ ) ); 
// prints ["maaaaa", indes: 10, ...]
//which means we have a match at index 10

// to match empty space followed by 4 x 'a'
console.log( str.match(/\sa{4}/ ) ); 
// prints [" aaaa", index: 19, ...]
// match at index 19

let str = "ama balo maaaaamal"; 
console.log( str.match( /a+/g ) ); 
// ["a", "a", "aa", "aaaaa", "a"]

console.log( str.match( /a/g ) ); 
// ["a", "a", "a", "a", "a", "a", "a", "a", "a", "a"]

let str = "aaa"; 
console.log( str.match( /a*/g ) ); 
// ["aaa", ""]

consolle.log( str.match( /a/g ) ); 
// ["a", "a", "a"]

let str = "aaa"; 
console.log( str.match( /a?/g ) ); 
// ["a", "a", "a", ""]

let str = "IsFunBaloonIsLearningRegExIsLean"; 

console.log (str.match( /Is(?=Learning)/ ) ); 
//["Is", index: 11, ...]
//Matches the 2nd "Is", right before "Learning"

console.log( str.match( /Is(?=Lean)/ ) ); 
//["Is", index: 26, ...]
//Match the 3rd "Is", right before "Lean"

console.log( str.match( /Is(?=L)/g ) ); 
// ["Is", "Is"]
//Matches all "Is" which are followed by "L"

console.log( str.match(/Is(?!L)/ ) ); 
//["Is", index:0, ...]
// Matches all "Is" which aren't followed by "L"

/(bam+)\w\1/g  same as 
/(bamm+)\w(bamm+)/g same as
/bamm+\wbamm+/g

/(\w+)\s(\1\1\1)\2/g same as
/(\w+)\s\1\1\1\1\1\1/g

/(\w+)\s\1\1\1/g  same as
/\w+\s\w+\w+\w+/g

let regex = /a[0-9]b+/

//if you want to pass flags (like i and g)
let regex = /a[0-9]b+/ig

  let regex - new RegExp('a[0-9]b+')

  //if you want to pass flags (like i and g)
  let regex = new RegExp('a[0-9]b+', 'ig')

// Difference between the two methods

let re = /bla/g; 
let str = "bla and yea bla yeh"; 

re.exec(str)
// -> ["bla", index: 0, ...]
re.exec(str)
// -> ["bla", index: 13, ...]
re.exec(str)
// -> null
re.exec(str)
// -> ["bla", index: 0, ...]                
// STARTS AGAIN

//USAGE WITH A LOOP
let match, str = "bla and yeah bla yeh ble"; 
while (mathc = re.exec(str)) {
    console.log(match); 
}
// ["bla", index: 0, input: ...]
// ["bla", index: 13, input: ...]

// on the other side, match works pretty simple
str.match(re)
// ["bla", "bla"]

let regexp = /bla/g; 
let str = 'bla and yeah bla yeh'; 
const matches = str.matchAll(regexp); 
for (let match of matches) {
    console.log(match)
}
// ["bla", index: 0, ...]
// ["bla", index: 13, ...]

  let str = "stuffed str living fforever pff"
  let regex = /f+/; //match one or more 'f'

  let repl = str.replace(regex, '*'); 
  //repl is "stu*ed str living fforeverpff"
  let repl = str.replaceAll(regex, '*'); 
  // repl is "stu*ed str living *orever p*"
  // NOTE: If you add g flag to replace it works like replaceAll