JavaScript Data Types
AJavaScript variable can hold8 types of data.
7 Primitive Data Types and1 Object Data Type.
The Object data type can hold many different object types.
| Type | Description |
|---|---|
| Number | A number representing a mathematical value |
| Bigint | A number representing a large integer |
| String | A text of characters enclosed in quotes |
| Boolean | A data type representing true or false |
| Undefined | A primitive variable with no assigned value |
| Null | A primitive value representing object absence |
| Symbol | A unique and primitive identifier |
| Object | A collection of key-value pairs of data |
Examples
let length = 16;
let weight = 7.5;
// BigInt
let x = 1234567890123456789012345n;
let y = BigInt(1234567890123456789012345)
// Strings
let color = "Yellow";
let lastName = "Johnson";
// Boolean
let x = true;
let y = false;
// Undefined
let x;
let y;
// Null
let x = null;
let y = null;
// Symbol
const x = Symbol();
const y = Symbol();
// Object
const person = {firstName:"John", lastName:"Doe"};
// Array Object
const cars = ["Saab", "Volvo", "BMW"];
// Date Object
const date = new Date("2022-03-25");
The Concept of Data Types
In programming, data types is an important concept.
To be able to operate on variables, it is important to know something about the type.
Without data types, a computer cannot safely solve this:
Does it make any sense to add "Volvo" to sixteen? Will it produce an error or will it produce a result?
JavaScript will treat the example above as:
Note
When adding a number and a string, JavaScript will treat the number as a string.
JavaScript evaluates expressions from left to right. Different sequences can produce different results:
#"tryit.asp?filename=tryjs_datatypes_addstrings_1">Try it Yourself »
#"tryit.asp?filename=tryjs_datatypes_addstrings_2">Try it Yourself »
In the first example, JavaScript treats 16 and 4 as numbers, until it reaches "Volvo".
In the second example, since the first operand is a string, all operands are treated as strings.
JavaScript Types are Dynamic
JavaScript has dynamic types. This means that the same variable can be used to hold different data types:
Example
x = 5; // Now x is a Number
x = "John"; // Now x is a String
JavaScript Strings
A string (or a text string) is a series of characters like "John Doe".
Strings are written with quotes. You can use single or double quotes:
Example
let carName1 = "Volvo XC60";
// Using single quotes:
let carName2 = 'Volvo XC60';
You can use quotes inside a string, as long as they don't match the quotes surrounding the string:
Example
let answer1 = "It's alright";
// Single quotes inside double quotes:
let answer2 = "He is called 'Johnny'";
// Double quotes inside single quotes:
let answer3 = 'He is called "Johnny"';
JavaScript Numbers
All JavaScript numbers are stored as decimal numbers (floating point).
Numbers can be written with, or without decimals:
Exponential Notation
Extra large or extra small numbers can be written with scientific (exponential) notation:
Number Types
Most programming languages have many number types:
Whole numbers (integers):
byte (8-bit),short (16-bit),int (32-bit),long (64-bit)
Real numbers (floating-point):
float (32-bit),double (64-bit).
Javascript numbers are always double (64-bit floating point).
Learn More:
JavaScript BigInt
All JavaScript numbers are stored in a 64-bit floating-point format.
JavaScript BigInt is a new datatype (ES2020) that can be used to store integer values that are too big to be representedby a normal JavaScript Number.
Learn More:
JavaScript Booleans
Booleans can only have two values:true orfalse.
Example
let y = 5;
let z = 6;
(x == y) // Returns true
(x == z) // Returns false
Booleans are often used in conditional testing.
Learn More:
JavaScript Objects
JavaScript Objects representcomplex data structures and functionalities beyond theprimitive data types (string, number, boolean, null, undefined, symbol, bigint).
JavaScript objects are written with curly braces{ }.
JavaScript objects contains a collection of differentproperties.
Object properties are written asname:value pairs, separated by commas.
Example
Create a person object with 4 properties: firstName, lastName, age and eyeColor:
Learn More:
Built-In Object Types
A JavaScript object can represent aJavScript object or aUser defined object.
Built-in JavavaScript object types can be:
| Object | The fundamental building block for complex data |
| Array | Object of values accessed by a numerical index |
| Date | Object for working with dates and times |
| RegExp | Object for working with regular expressions |
| Map | Object of key-value pairs where the keys can be of any data type |
| Set | Object of values where each value can only appear once |
| Error | Object represents error conditions during program execution |
| Promise | Object representing the completion or failure of an asynchronous operation |
| Int8Array | Array for storing fixed-size 8-bits integer values |
| Int16Array | Array for storing fixed-size 16-bits integer values |
| Int32Array | Array for storing fixed-size 32-bits integer values |
| Float16Array | Array for storing fixed-size 16-bits floating-point values |
| Float32Array | Array for storing fixed-size 32-bits floating-point values |
| Float64Array | Array for storing fixed-size 64-bits floating-point values |
| BigInt64Array | Array for storing fixed-size 64-bits big integer values |
Note
The list above is not complete,as JavaScript offers other built-in object types like Math for mathematic methods and values,and various other specialized objects for specific tasks.
The typeof Operator
You can use the JavaScripttypeof operator to find the type of a JavaScript variable.
Thetypeof operator returns the type of a variable or an expression:
Example
typeof "John" // Returns "string"
typeof "John Doe" // Returns "string"
Example
typeof 314 // Returns "number"
typeof 3.14 // Returns "number"
typeof (3) // Returns "number"
typeof (3 + 4) // Returns "number"
Learn More:
JavaScript Arrays
JavaScript arrays are a special type of JavaScript objects.
JavaScript arrays are written with square[ ] brackets.
Array items are separated by commas.
The following code declares (creates) an array calledcars, containing three items (car names):
Array indexes are zero-based, which means the first item is [0], second is [1], and so on.
Learn More:
Undefined
In JavaScript, a variable without a value, has the valueundefined. The type is alsoundefined.
Any variable can be emptied, by setting the value toundefined. The type will also beundefined.
Empty Values
An empty value has nothing to do withundefined.
An empty string has both a legal value and a type.
Datatype null
In JavaScript, a variable or an expression can obtain the datatype null in several ways.
A function can return null or a variable can be assigned the null value:
Note
Thetypeof operator returnsobject for null.
This is a historical quirk in JavaScript and does not indicate that null is an object.
Thestrict equality operator (===) compares both the value and the type of the operands.
It returnstrue only if both the operands values and types arenull.
Theloose equality operator (==) also returnstruefor anull value,but it also returns true if the value isundefined.
Using == is not recommended when checking fornull.
