pattern matching in javascript code example

Example 1: javascript regex

//Declare Reg using slash
let reg = /abc/
//Declare using class, useful for buil a RegExp from a variable
reg = new RegExp('abc')

//Option you must know: i -> Not case sensitive, g -> match all the string
let str = 'Abc abc abc'
str.match(/abc/) //Array(1) ["abc"] match only the first and return
str.match(/abc/g) //Array(2) ["abc","abc"] match all
str.match(/abc/i) //Array(1) ["Abc"] not case sensitive
str.match(/abc/ig) //Array(3) ["Abc","abc","abc"]
//the equivalent with new RegExp is
str.match('abc', 'ig') //Array(3) ["Abc","abc","abc"]

Example 2: javascript regex reference

// Javascript Regex Reference
//  /abc/	A sequence of characters
//  /[abc]/	Any character from a set of characters
//  /[^abc]/	Any character not in a set of characters
//  /[0-9]/	Any character in a range of characters
//  /x+/	One or more occurrences of the pattern x
//  /x+?/	One or more occurrences, nongreedy
//  /x*/	Zero or more occurrences
//  /x?/	Zero or one occurrence
//  /x{2,4}/	Two to four occurrences
//  /(abc)/	A group
//  /a|b|c/	Any one of several patterns
//  /\d/	Any digit character
// /\w/	An alphanumeric character (“word character”)
//  /\s/	Any whitespace character
//  /./	Any character except newlines
//  /\b/	A word boundary
//  /^/	Start of input
//  /$/	End of input

Example 3: how to use the match function in javascript for regex

const str = 'For more information, see Chapter 3.4.5.1';
const re = /see (chapter \d+(\.\d)*)/i;
const found = str.match(re);

console.log(found);

// logs [ 'see Chapter 3.4.5.1',
//        'Chapter 3.4.5.1',
//        '.1',
//        index: 22,
//        input: 'For more information, see Chapter 3.4.5.1' ]

// 'see Chapter 3.4.5.1' is the whole match.
// 'Chapter 3.4.5.1' was captured by '(chapter \d+(\.\d)*)'.
// '.1' was the last value captured by '(\.\d)'.
// The 'index' property (22) is the zero-based index of the whole match.
// The 'input' property is the original string that was parsed.

Example 4: regex for strings with specific letters javascript

let re = /ab+c/;