Lesson 17 — Regular expressions

Match patterns in text

A regular expression (regex) describes a text pattern between slashes, like /cat/. Special symbols make it powerful: ^ means "start of the text", $ means "end", [0-9] means any one digit, and + means "one or more of the previous". .test(text) returns true or false.

const hasCat = /cat/;
console.log(hasCat.test("my cat")); // true
console.log(/^a/.test("banana"));   // false — does not start with a

Why it matters: checking postcodes, phone numbers and passwords in forms is done with regex.