Datatypes

JavaScript provides different data types to hold different types of values. There are two types of data types in JavaScript.

  •    Primitive data type
  •    Non-primitive (reference) data type

JavaScript is a dynamic type language, means the type of the variable does not need to be explicitly specified.This is because the type of the variable is dynamically assigned by the javascript engine. A variable can be declared using the keyword var. var can hold any type of values such as numbers, strings etc.

There are five types of primitive data types in JavaScript.

  •     String- represents a sequence of characters e.g. "hello"
  •     Number- represents numeric values e.g. 100
  •     Boolean- represents boolean value either false or true
  •     Undefined- represents an undefined value
  •     Null- represents null i.e. no value at all
  •     The non-primitive data types are:
  •     Object- represents instance through which we can access members
  •     Array- represents a group of similar values
  •     RegExp- represents regular expression
     

Primitive data types:

String:

A string (or a text string) is a series of characters. Strings are written with quotes. They can be represented by using either of single or double quotes.

Example: 

var carName = "Volvo"; // Using double quotes 
var carName = 'Volvo'; // Using single quotes

Example:

<!DOCTYPE html>
<html>
<body>
<p id="demo"></p>
<script>
var carName = "Volvo";
var answer = 'Its alright';
document.getElementById("demo").innerHTML =
carName + "<br>" + 
answer;
</script>
</body>
</html>


Output:

Volvo
Its alright
 

Number:

JavaScript has only one type of numbers. Numbers can be written with, or without decimals.

Example:

var x1 = 34.00; // Written with decimals 
var x2 = 34; // Written without decimals

Note: Extra large or extra small numbers can be written with scientific (exponential) notation.

Example:

<!DOCTYPE html>
<html>
<body>
<p id="demo"></p>
<script>
var x1 = 34.00;
var x2 = 34;
var y = 123e5;
var z = 123e-5;
document.getElementById("demo").innerHTML = x1 + "<br>" + x2 + "<br>" + y + "<br>" + z
</script>
</body>
</html>

Output:

34
34
12300000
0.00123
 

Boolean:

Booleans can only have two values: true or false.

Example:

var x = true;
var y = false;
Booleans are often used in conditional testing.
 

Non-primitive data types:

Arrays

JavaScript arrays are written with square brackets. The items in the Array are separated by commas.

Example:

<!DOCTYPE html>
<html>
<body>
<p id="demo"></p>
<script>
var cars = ["Saab","Volvo","BMW"];
document.getElementById("demo").innerHTML = cars[0];
</script>
</body>
</html>
 

Output:

saab

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Objects

JavaScript objects are written with curly braces. 
Object properties are written in key:value pairs, which are separated by commas.

Example:

<!DOCTYPE html>
<html>
<body>
<p id="demo"></p>
<script>
var person = {
    firstName : "John",
    lastName  : "Doe",
    age       : 50,
    eyeColor  : "blue"
};
document.getElementById("demo").innerHTML =
person.firstName + " is " + person.age + " years old.";
</script>
</body>
</html>


Output:

John is 50 years old

The object (person) in the example above has 4 properties: firstName, lastName, age, and eyeColor.
 

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