This is going to be a little guide for , a very important part of programming in general. regular expressions I will try to be the more simple and clear as possible. I hope you like it 😊 What is a Regular Expression? Are within a text string. In JavaScript, regular expressions are also objects. patterns used to find a certain combination of characters Simple Creation: ✍️ ✔️: ️ Recommended way let re = /good/; ❌: Not so Recommended way let re = new RegExp(/good/); When is better to use the literal way or using the RegExp constructor? ❓ Use the when the regular expression is going to be , because this way offers the immediate compilation of the regular expression when the script is loaded. literal expression constant Use the constructor when the regular expressions is going to or maybe the user is going to determinate the pattern. RegExp change Let’s start with methods and properties: 👊🏻 Ways to prove a Regular Expression: Return an if exist a match, if not, return exec: array null. console.log(re.exec('good bye'));-> [ 'good', index: 0, input: 'good bye' ] So we get : [ ‘good’, index: 0, input: ‘good bye’ ] 'good' -> is the regular expression.index: -> Is when the regular expression starts.input: -> Is the actual exec text. Return if exist a match, if not, return . test: true false console.log(re.test('good job!'));-> trueconsole.log(re.test('nice job!'));-> falseconsole.log(re.test('Good bye'));-> false In the last example we get maybe you are asking why that happens if the word ‘good’ was included, the thing here is that , later, when we learn about we are going to fix this. false, regular expressions are case sensitive like default flags Return an or . match: array null let str = 'goodbye for everyone';console.log(str.match(re));-> [ 'good', index: 0, input: 'good bye for everyone' ] This one is very similar to , the difference here is that we change the way that the regular expression is tested. exec Return the of the first match, if there is not match return search: index -1 let str = 'goodbye for everyone';console.log(str.search(re));-> 0 (because 'good' starts at the beginning of the text) let str2 = 'that is not good';console.log(str2.search(re));-> 12 Return a if there find the regular expression. replace: new string let str = 'good job everyone!';console.log(str.replace(re, 'nice'));-> nice job everyone! 🚩 Flags: The flags are included at the end of the regular expression: Literal Expression: let re = /pattern/flags; With RegExp: let re = new RegExp('pattern', 'flags'); There is four flags to use: Is for global search. Meaning it’ll match all occurrences, not just the first. **g** : let str = 'aaa'; console.log(str.match(/a/g)); -> [ 'a', 'a', 'a' ] // Without the g flagconsole.log(str.match(/a/));-> [ 'a', index: 0, input: 'aaa' ] Is for case-insensitive. **i** : let re = /good/i;console.log(re.test('Good bye'));-> true There is also two more: : for multi-line searching. **m** call Sticky, matches only from the index indicated by the property of this regular expression. (not standard yet). **y** : lastIndex Properties: 🌳 Get the source text: let re = /good/;console.log(re.source);-> good Return the flags that the regular expression have: let re = /good/i;console.log(re.flags);-> i Verify if the regular expression is case-sensitive (i) or not: let re = /good/i;console.log(re.ignoreCase);-> true let re2 = /good/;console.log(re2.ignoreCase);-> false Verify if the regular expression have the global (g) flag: let re = /good/g;console.log(re.global);-> true Verify if the regular expression have the multiline (m) flag: let re = /good/m;console.log(re.multiline);-> true Verify if the regular expression have the sticky (y) flag: let re = /good/y;console.log(re.sticky);-> true Metacharacters Symbols: 🔱 There are quite a few special characters that will help us significantly when it comes to building our regular expressions. **^** : Must start with: let re = /^j/;console.log(re.test('javascript'));-> trueconsole.log(re.test('object'));-> false **$** : Ends with: let re = /.com$/;console.log(re.test('germancutraro@hotmail.com'));-> trueconsole.log(re.test('germancutraro@hotmail'));-> false **.** : Any ONE character: let re = /go.od/;console.log(re.test('go@od'));-> trueconsole.log(re.test('go@#od'));-> false ***** : Any character, could be 0 or more times repeated: let re = /go*od/;console.log(re.test('good'));-> trueconsole.log(re.test('goXdod'));-> falseconsole.log(re.test('god'));-> true **?** : Define optional characters: let re = /go?o?d/;console.log(re.test('god'));-> trueconsole.log(re.test('grfy'));-> false **\** : Escape character: let re = /go?o\?d/;console.log(re.test('god'));-> false **[]** : Character sets: let re = /gr[ae]y/;console.log(re.test('gray'));-> trueconsole.log(re.test('grey'));-> trueconsole.log(re.test('grty'));-> false : **[^_characters_]** Match everything except the characters: let re = /[^F]riday/;console.log(re.test('Friday'));-> falseconsole.log(re.test('Nriday'));-> true **[_range_]** : Match a range of characters let reU = /[A-Z]riday/; // any capitalize letter ([A-Z])console.log(reU.test('Friday'));-> truelet reL = /[a-z]riday/; // any lower case letter ([a-z])console.log(reL.test('friday'));-> truelet reUL = /[A-Za-z]riday/; // any letterconsole.log(reUL.test('%riday'));-> falselet reAny = /[0-9]riday/; // any numberconsole.log(reAny.test('3riday'));-> true **{}** : let re = /go{2}d/;console.log(re.test('good'));-> trueconsole.log(re.test('god'));-> false // In this case means that the string must have two 'o' (the character before the curly braces). let re2 = /go{2,4}d/;console.log(re.test('good'));-> trueconsole.log(re.test('god'));-> falseconsole.log(re.test('goood'));-> true // Now, in re2, could be between 2 and 4 'o' (be careful with the space, {2, 4} is not valid -> ) the space after the coma is not valid let re3 = /go{2,}d/;console.log(re3.test('goooooooooood'));-> trueconsole.log(re3.test('god'));-> false // In the last example could be 2 or more. 🔑 Shorthands: Some Classes Shorthands: : Word or number (alphanumeric) . /\a/ : One or more. /a+/ : Non-Word character. /\W/ : Match any number digit. /\d/ : Match any number digit 0 or more times. /\d+/ : Non-Number digit. /\D/ : Match whitespace. /\s/ : Non-whitespace. /\S/ : Match only if ‘y’ is followed by ‘e’ /y(?=e)/ : Match only if ‘y’ is followed by ‘e’ /y(?=!e)/ not Follow me on: Github And there is much more about regular expression, but I hope this may have helped! I want to mention and thank to: Brad Traversy
