JavaScript Data Types Explained

Learn about data types in JavaScript in this JS Quickie

JavaScript Data Types Explained

Two Kinds of Data

In JavaScript there are two different kinds of data: primitives, and objects. A primitive is simply a data type that is not an object, and has no methods.

In JS, there are six primitive data types:

• Boolean
• Number
• String
• Null
• Undefined
• Symbol

Boolean

A boolean represents only one of two values: true, or false. Think of a boolean as an on/off or a yes/no switch.

var boo1 = true;
var boo2 = false;

Number

There is only one type of Number in JavaScript. Numbers can be written with or without a decimal point. A number can also be +Infinity, -Infinity, and NaN (not a number).

var num1 = 32;
var num2 = +Infinity;

String

Strings are used for storing text. Strings must be inside of either double or single quotes. In JS, Strings are immutable (they cannot be changed).

var str1 = 'hello, it is me';
var str2 = "hello, it's me";

Null

Null has one value: null. It is explicitly nothing.

var nothing = null;

Undefined

A variable that has no value is undefined.

var testVar;
console.log(testVar); // undefined

Symbol

Symbols are new in ES6. A Symbol is an immutable primitive value that is unique. For the sake of brevity, that is the extent that this article will cover Symbols.

const mySymbol = Symbol('mySymbol');

What about Objects?

Objects are not a primitive data Type.

An object is a collection of properties. These properties are stored in key/value pairs. Properties can reference any type of data, including objects and/or primitive values.

var obj = {
  key1: 'value',
  key2: 'value',
  key3: true,
  key4: 32,
  key5: {}
}

Loosely Typed

JavaScript is a loosely typed language. This means you don’t have to declare a variable’s type. JavaScript automatically determines it for you. It also means that a variables type can change. Let’s look at an example:

We’ll create a variable named car and set it equal to a string value:

var car = 'ford';

Later, we realize we want the value of car to be the year it was made, so we change car to a number:

car = 1998;

It works — and JavaScript could care less. Because JS is loosely typed, we are free to change variable types as we please.

Closing Notes:

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If you want to improve your JavaScript Skills even more, check out: A Beginners Guide to Advanced JavaScript

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