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JS TutorialLesson #100

JavaScript Data Types

A JavaScript variable can hold 8 types of data.

A JavaScript variable can hold 8 types of data.

7 Primitive Data Types and 1 Object Data Type.

The Object data type can hold many different object types.

Type	Description
Number	A number representing a numeric 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 variable with no assigned value
Null	A value representing object absence
Symbol	A unique primitive identifier
Object	A collection of key-value pairs of data

Examples

Example Code

javascript

Try it Yourself

// Number

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:

Example

Example Code

javascript

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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:

Example

Example Code

javascript

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let x = "16" + "Volvo";

When adding a number and a string, JavaScript will treat the number as a > string.

Example

Example Code

javascript

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let x = 16 + "Volvo";

Example

Example Code

javascript

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let x = "Volvo" + 16;

JavaScript evaluates expressions from left to right. Different sequences can produce different results:

JavaScript:

Example Code

javascript

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let x = 16 + 4 + "Volvo";

JavaScript:

Example Code

javascript

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let x = "Volvo" + 16 + 4;

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

Example Code

javascript

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let x;       // Now x is undefined

x = 5;       // Now x is a Number

x = "John";  // Now x is a String

Built-In Object Types

A JavaScript object can represent a JavScript object or a User defined object.

Built-in JavaScript object types can be:

Object	Description
Array	Array of values accessed by a numerical index
Map	Array of key-value pairs where the keys can be of any data type
Set	Array of values where each value can only appear once
WeakMap	A type of Map with weak references to the stored objects.
WeakSet	A type of Set with weak references to the stored objects.
Math	An object that provides math constants and functions like PI and random()
Date	Object for working with dates and times
RegExp	Object for working with regular expressions
Error	Object represents error conditions during program execution
JSON	Object with methods for parsing values between JSON and objects
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

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

Example Code

javascript

Try it Yourself

typeof ""          // Returns
 "string"

typeof "John"      // Returns
 "string"

typeof "John Doe"  // Returns
 "string"

Example

Example Code

javascript

Try it Yourself

typeof 0           // Returns
 "number"

  typeof 314         // Returns
 "number"

  typeof 3.14        // Returns
 "number"

  typeof (3)         // Returns
 "number"
typeof (3 + 4)     // Returns
 "number"

JavaScript syntax and algorithm demonstration.

let x = 16 + 4 + "Volvo";

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