JavaScript has 8 Datatypes
A 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 |
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:
typeof "" // Returns
"string"
typeof "John" // Returns
"string"
typeof "John Doe" // Returns
"string"typeof 0 // Returns
"number"
typeof 314 // Returns
"number"
typeof 3.14 // Returns
"number"
typeof (3) // Returns
"number"
typeof (3 + 4) // Returns
"number"JavaScript Strings
A string (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';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"';You will learn a lot more about JavaScript 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;Exponential Notation
Extra large or extra small numbers can be written with scientific (exponential) notation:
Example
let y = 123e5; // 12300000
let z = 123e-5; // 0.00123JavaScript Booleans
JavaScript booleans can only have one of two values: true or false
The boolean value of an expression is the basis for JavaScript comparisons.
Given that x = 5 , the table below explains comparison:
| Description | Expression | Returns |
|---|---|---|
| Equal to | (x == 8) | false |
| Not equal to | (x != 8) | true |
| Greater than | (x > 8) | false |
| Less than | (x < 8) | true |
Example
let x = 5;
(x == 8); // equals false
(x != 8); // equals trueAll JavaScript comparison operators (like ==, !=, <, >) return true or false from the comparison.
Datatype undefined
In computer programs, variables are often declared without a value. The value can be something that has to be calculated, or something that will be provided later, like user input.
A variable without a value has the datatype undefined .
A variable without a value also has the value undefined .
Example
let carName;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"You will learn a lot more about Data Types later in this tutorial.