There are two data types in JavaScript: primitives and objects.
Primitive values are atomic data that is passed by value and compared by value. The following are the primitive types:
booleanstringnumberundefinednullsymbolObjects, on the other hand, are compound pieces of data that are passed by reference and compared by reference.
typeof operatorYou can check the type of a value by using the typeof operator
console.log(typeof "two"); // string
console.log(typeof 2); // number
console.log(typeof true); // boolean
console.log(typeof undeclaredVariable); // undefined
console.log(typeof { value: 2 }); // objectSee typeof on MDN web docs for more details.
The Boolean type is similar to most other programming languages with two options: true or false.
let isRequired = true;
let isOptional = false;See Boolean on MDN web docs for more details.
To be discussed shortly.
To be discussed shortly.
The three primitive types string, number and boolean have corresponding types whose instances are objects: String, Number, Boolean.
const name = "Ali";
const firstname = new String("Ali");
console.log(name); // Ali
console.log(firstname); // Ali
console.log(typeof name); // string
console.log(typeof firstname); // object
console.log(name instanceof String); // false
console.log(firstname instanceof String); // trueYou can use the instanceof operator to check the type of an object.
undefined and nullJavaScript has two “bottom” values!
undefined.null value denotes an “intentionally” absent value.Although you can, don’t deliberately set a value to undefined!
JavaScript has lots of quirks, and a bunch of them are around null and undefined (and how they behave, relate, and differ). We will see some of these in later sections. For now, enjoy this!
console.log(typeof undefined); // undefined
console.log(typeof null); // objectFor more details, Brandon Morelli has a nice article: JavaScript — Null vs. Undefined. For a complete reference, visit null and undefined on MDN web docs.
The symbol is a new addition to the JavaScript language, which enables Metaprogramming. It is beyond the scope of this course. You can consult the following resources if you are interested to learn more.