basic-regular-expressions.js

let re = /hello/i; //insensitive

// Meta chars
re = /^h/; // Starts with lower case h => false
re = /^h/i; // Starts with any case h => true
re = /--$/i; // end with -- => true
re = /^--$/i; // must begin and end with -- => false
re = /w.rld/i; // matches any ONE char => true
re = /w*d/i; // matches any char 0 or more times => true
re = /w?rld/i; // matches optional character => true
re = /s*thing\?/i; // escape character matches literal '?' => true

//brackets - character sets
re = /w[0o]rld/; // matches either 0 or o characters between => true
re = /w[^0o]rld/; // matches anything but 0 or o characters => false
re = /w[A-F]rld/; // matches any uppercase letter => false
re = /w[a-f]rld/; // matches any lowercase letter => false
re = /w[A-Fa-f0-9]rld/; // matches any uppercase, lowercase, or number letter => true

//braces {} - Quantifiers
re = /wil{2}ows/; // char before must occur 2 times => true
re = /wil{2,4}ows/; // char before must occur 2-4 times => true
re = /wil{3,}ows/; // char before must occur at least 3 times => false

// Parenthesis () - Grouping
re = /([0-9][X-Z]){3}/; // matches number 0-9 followed by either X,Y, or Z 3 times => true

// Shorthand Character Classes
re = /\w/ // word character or _ => true
re = /\w+/ // one or more word characters => true
re = /\W/ // non word characters => true
re = /\d/ // digits => true
re = /\d+/ // digits on or more times => true
re = /\D/ // non digits anything but 0-9 => true
re = /\s/ // white space => true
re = /\S/ // non white space => true
re = /will\b/ // word boundary "will" => true

// Assertions
re = /o(?=ws)/ // Match "o" followed by a "ws" => true
re = /some(?!\s)/ // Match "some" NOT followed by whitespace => true

const str = 'Hello w0rld there willows 5X5Y5Z will is, **something?--';

has(re, str);
function has(regEx, str) {
    console.log(regEx.test(str));
}