Data Types: string number boolean null undefined
Explore JavaScript's primitive types, use typeof to inspect them, and learn the difference between null and undefined.
JavaScript's Type System
JavaScript is dynamically typed — variables don't have types, values do. The same variable can hold a string, then a number, then null. Understanding the seven primitive types prevents a huge class of bugs.
string
Strings represent text. Use single quotes, double quotes, or backtick (template literal). They are immutable — string methods return new strings. Strings have a .length property and many built-in methods.
const greeting = 'Hello';
const lang = "JavaScript";
const sentence = `I love ${lang}`; // template literal
console.log(greeting.length); // 5
console.log('hello'.toUpperCase()); // 'HELLO'
console.log(' trim me '.trim()); // 'trim me'All lessons in this course
- Variables: let const var and Scope
- Data Types: string number boolean null undefined
- Functions: declarations expressions arrow functions
- Control Flow: if else switch for while