regex.js

// RegEx
// Sample: /expression/.test('string');
// 1. expression: is any regular expression that we build
// 2. string: it is a string that we put under test
// 3. test: this method returns true or false
// / & /: mark the start and end of the expression
// expression between / are literals. They are treated as literals characters.


// Start with single character
/a/.test("a"); //true
/a/.test("b"); // false

// Find a string which has a particular character for eg: a
/a/.test("abc"); // true
/a/.test("bcd"); // false
/a/.test("cba"); // true

var e = /a/;
e.test("abc"); // true
e.test("bcd"); // false
e.test("cba"); // true

// Reach Multi Character
/ab/.test("abacus"); // true
/bac/.test("abacus"); // true
/abc/.test("abacus"); // false (No pattern of abc was found)
/abas/.test("abacus"); // false (No pattern of abas was found)

// Patterns in Number
var b = /0|1|2|3|4|5|6|7|8|9/; // | (pipe) means OR
b.test("42"); // true
b.test("The answer is 42"); // true => Shouldn't be true.


var c = /[0123456789]/; // 9 pipes were removed with two square brackets
c.test("42"); // true
c.test("The number is 42"); // true

var d = /[0-9]/;
d.test("42"); // true
d.test("The number is 42"); // true

// The prefix and suffix patterns

// PREFIX: any character that follow ^ should be at the start of the string.
/^a/.test("abc"); // true => a is in the start of the string
/^a/.test("bca"); // false => a is not in the start of the string
/^http/.test("https://pineboat.in"); // true
/^http/.test("ftp://pineboat.in"); // false

// SUFFIX: this pattern follows $ at the end of the pattern to be test directs the test to look for end of the string
// Look for string that ends with js
/js$/.test("regex.js"); // true

/js$/.test("regex.sj"); // false

var f = /^[0-9]$/;
f.test("42"); // false
f.test("The answer is 42"); // false
f.test("7"); // true
f.test(7); // true