JavaScript Data Types
JavaScript has 8 Datatypes
1. String
2. Number
3. Bigint
4. Boolean
5. Undefined
6. Null
7. Symbol
8. Object
The Object Datatype
The object data type can contain:
1. An object
2. An array
3. A date
Examples
// Numbers:
let length = 16;
let weight = 7.5;
// Strings:
let color = "Yellow";
let lastName = "Johnson";
// 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");
Note
A JavaScript variable can hold any type of data.
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.
Example
let x = 16 + "Volvo";
Try it Yourself »
Example
let x = "Volvo" + 16;
Try it Yourself »
JavaScript evaluates expressions from left to right. Different sequences can
produce different results:
JavaScript:
let x = 16 + 4 + "Volvo";
Result:
20Volvo
Try it Yourself »
JavaScript:
let x = "Volvo" + 16 + 4;
Result:
Volvo164
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
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 »
You will learn more about strings later in this tutorial.
JavaScript Numbers
All JavaScript numbers are stored as decimal numbers (floating point).
Numbers can be written with, or without decimals:
Example
// With decimals:
let x1 = 34.00;
// Without decimals:
let x2 = 34;
Try
it Yourself »
Exponential Notation
Extra large or extra small numbers can be written with scientific
(exponential) notation:
Example
let y = 123e5; // 12300000
let z = 123e-5; // 0.00123
Try
it Yourself »
Note
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 one type:
double (64-bit floating point).
You will learn more about numbers later in this tutorial.
JavaScript BigInt
All JavaScript numbers are stored in a 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.
Example
let x = BigInt("123456789012345678901234567890");
Try
it Yourself »
You will learn more about BigInt later in this tutorial.
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.
You will learn more about booleans later in this tutorial.
JavaScript Arrays
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):
Example
const cars = ["Saab", "Volvo", "BMW"];
Try it Yourself »
Array indexes are zero-based, which means the first item is [0], second is
[1], and so on.
You will learn more about arrays later in this tutorial.
JavaScript Objects
JavaScript objects are written with curly braces {}.
Object
properties are written as name:value pairs, separated by commas.
Example
const person = {firstName:"John", lastName:"Doe", age:50, eyeColor:"blue"};
Try it Yourself »
The object (person) in the example above has 4 properties: firstName,
lastName, age, and eyeColor.
You will learn more about objects later in this tutorial.
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 »
You will learn more about typeof later in this tutorial.
Undefined
In JavaScript, a variable without a value, has the value undefined.
The type is also undefined.
Example
let car; // Value is undefined,
type is undefined
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Any variable can be emptied, by setting the value to undefined.
The type will also be undefined.
Example
car = undefined; // Value is undefined,
type is undefined
Try it Yourself »
Empty Values
An empty value has nothing to do with undefined.
An empty string has both a legal value and a type.
Example
let car = ""; //
The value is
"", the typeof is "string"
Try it Yourself »
Test Yourself With Exercises
Exercise:
Use comments to describe the correct data type of the following variables:
let length = 16; //
let lastName = "Johnson"; //
const x = {
firstName: "John",
lastName: "Doe"
}; //
Submit Answer »
Start the Exercise
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Reference: https://www.w3schools.com/js/js_datatypes.asp