JavaScript Data Types
JavaScript has 8 DatatypesA JavaScript variable can hold 8 types of data: | |
| Type | Description |
|---|---|
| String | A text of characters enclosed in quotes |
| Number | A number representing a mathematical value |
| Bigint | A number representing a large integer |
| Boolean | A data type representing true or false |
| Object | A collection of key-value pairs of data |
| Undefined | A primitive variable with no assigned value |
| Null | A primitive value representing object absence |
| Symbol | A unique and primitive identifier |
Examples
// Strings
let color = "Yellow";
let lastName = "Johnson";
// Numbers
let length = 16;
let weight = 7.5;
// Bigint
let x = 1234567890123456789012345n;
let y = BigInt(1234567890123456789012345)
// Booleans
let x = true;
let y = false;
// Object
const person = {firstName:"John", lastName:"Doe"};
// Array object
const cars = ["Saab", "Volvo", "BMW"];
// Date object
const date = new Date("2022-03-25");
// Undefined
let x;
let y;
// Null
let x = null;
let y = null;
// Symbol
const x = Symbol();
const y = Symbol();
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:
let x = 16 + "Volvo";
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:
let x = "16" + "Volvo";
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:
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
let x; // Now x is undefined
x = 5; // Now x is a Number
x = "John"; // Now x is a String
Try
it Yourself »
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
// Using double quotes:
let carName1 = "Volvo XC60";
// Using single quotes:
let carName2 = 'Volvo XC60';
Try
it Yourself »
You can use quotes inside a string, as long as they don't match the quotes surrounding the string:
Example
// Single quote inside double quotes:
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"';
Try
it Yourself »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 represented by a normal JavaScript Number.
Learn More:
JavaScript Booleans
Booleans can only have two values: true or false.
Example
let x = 5;
let y = 5;
let z = 6;
(x == y)
// Returns true
(x == z) // Returns
false
Try it Yourself »Booleans are often used in conditional testing.
Learn More:
JavaScript Objects
JavaScript Objects represent complex data structures and functionalities beyond the primitive data types (string, number, boolean, null, undefined, symbol, bigint).
JavaScript objects are written with curly braces { }.
JavaScript objects contains a collection of different properties.
Object properties are written as name:value pairs, separated by commas.
Example
Create a person object with 4 properties: firstName, lastName, age and eyeColor:
const person = {firstName:"John", lastName:"Doe", age:50, eyeColor:"blue"};
Try it Yourself »
Learn More:
Built-In Object Types
A JavaScrip object can represent a JavScript objects or and user 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 JavaScript typeof operator to find the type
of a JavaScript variable.
The typeof operator returns the type of a variable or an expression:
Example
typeof "" // Returns
"string"
typeof "John" // Returns
"string"
typeof "John Doe" // Returns
"string"
Try it Yourself »
Example
typeof 0 // Returns
"number"
typeof 314 // Returns
"number"
typeof 3.14 // Returns
"number"
typeof (3) // Returns
"number"
typeof (3 + 4) // Returns
"number"
Try it Yourself »
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 called cars, 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 value undefined.
The type is also undefined.
Any variable can be emptied, by setting the value to undefined.
The type will also be undefined.
Empty Values
An empty value has nothing to do with undefined.
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
The typeof operator returns object for null.
This is a historical quirk in JavaScript and does not indicate that null is an object.
The strict equality operator (===) compares both the value and the type of the operands.
It returns true only if both the operands values and types are
null.
The loose equality operator (==) also returns true
for a null value,
but it also returns true if the value is undefined.
Using == is not recommended when checking for null.
