JavaScript - SPLessons

JavaScript DataTypes

Chapter 7

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JavaScript DataTypes

JavaScript DataTypes

shape Introduction

As discussed in the previous chapters, JavaScript is a dynamic scripting language, which can assign the data type to a variable dynamically. This interpretation of datatype to a variable is done by JavaScript script engine. Now, lets take a look at various JavaScript DataTypes.

shape Description

To hold different types of values, data types are used in JavaScript. The JavaScript DataTypes are basically divided into three types. They are:

shape Conceptual
figure

Primitive Datatypes

shape Description

Primitive datatypes are the basic data types in JavaScript and are classified into 3 types:

Number type

Numbers can contain various values. To create a number, a variable with var keyword has to be created and value has to be stored in it.

  • Decimal value: A number with a normal value can be as follows.
    Var b=25;
  • Octal number: JavaScript can convert the octal value to decimal value. A number with octal value(a number with 8 digits from 0-7) can be as follows.
    var b=012; //contains the decimal value 10
  • Hexadecimal number: Hexadecimal value can be created using 0x and can be as follows.
    var myHex1=0xF; //contains decimal value 15
  • Floating point number: These are defined by placing the numbers after the decimal point.
    var d=2.6;
    var e=.6; // valid but not recommended
    var f=3.; // considered as 3 only
    var g=5.0; //considered as 5 only
    var f=6e5; // the output will be 60000. Large/small numbers can use e to represent.
    var h=2e-4; // the output will be 0.0002
  • IsFinite(): IsFinite() function gives the result in the form of boolean. If the number is finite, then the result will be true, if not, the result will be false.
    var num1=2*Number.MAX_VALUE; //infinite number
    var test=isFinite(num1); //false
  • NaN (Not a Number): In this case, the result will not be a number.
    var num2=”Orange”/5;

Below example shows numbers and various types in it.

<!DOCTYPE html>
<html>
	<head>
		<title> variables test</title>;
		 
		<h2> Welcome to Splessons</h2>;
	 
	</head>
	<body>
		<script type="text/javascript">
			 
			//decimal value
			var a=5;
			document.write("Your number is ", a);
			 
			//Octal value
			var b=012;
			document.write("Octal number is", b); 
			 
			//Hexadecimal value
			var c=0xF;
			document.write("Hexadecimal number is", c);
			 
			//Floating point values
			var d=2.6;
			document.write("Float point is",d);
			var e=.6;
			document.write("Float point is",e);
			var f=3.;
			document.write("Float point is",f);
			var g=5.0;
			document.write("Float point is",g);
			var h=6e5;
			document.write("Float point is",h);
			var i=2e-4;
			document.write("Float point is",i);
			 
			//calculating sum of two floating points
			var sum=d+g;
			document.write("The sum is ",sum);
			 
			//isInfinite() function and the range
			var num1=2*Number.MAX_VALUE; 
			var res=isFinite(num1); 
			document.write("The number is infinite and hence result is ",res);
			 
			//NaN
			var num2="Orange"/5;
			document.write("", num2);
		</script>
	</body>
</html>

Output: 

String type

Text in JavaScript is called as “Strings” and is a sequence of characters. To store the string value in a variable, it must be enclosed between double quotes (” “) or single quotes(‘ ‘). But, the quotes must be consistent. If started with single quote, one should end with single quote only.

var a=”splessons”; //valid
var b=”splessons”; //valid

var a=’splessons”; //invalid
var b=”splessons’; //invalid

  • String Escape Sequences: Escape sequences are used when want to encode and include some special characters in Strings.
    Literal Function Example Output
    \n New line var msg=”Hello\nWorld”; Hello
    World
    \t Tab space var msg=”Hello\tWorld”; Hello World
    \b Backspace var msg=”Hello\bWorld”; HelloWorld
    \r Carriage return var msg=”Hello\rWorld”; Hello World
    \\ Backslash with string var msg=”Hello\\World”; Hello\World
    \’ Single quote on screen var msg=”\’Hello\’ World”; ‘Hello’ World
    \” Double quote on screen var msg=”\”Hello\”World”; “Hello”World
    \x Hexadecimal value depending on ASCII value var msg=”\x41 book”; A book
    \unnnn Unicode characters on screen var msg=”\u03a3 World”; Σ World
  • String Conversion: The values of other data types can be converted to strings. A string can be concatenated with other string using +.

    var a=”Hello”;
    a=a+”World”; // outputs is Hello World

    Conversion to string using toString().

    var a=15;
    var b=a.toString(); //b contains string 15
    var c=a.tostring(2); //prints 1111(binary value)

Boolean Type

Boolean type can be used to test the conditions and has only two values-true and false. Any value in JavaScript can be converted into boolean using Boolean() function.

var a;
var res=Boolean(a); //a doesn’t have any value and hence undefined

var a=null;
var res=Boolean(a); //output is false since null converts to false

var a=””;
var res=Boolean(a); //output is falsie since empty string converts to false

var a=0;
var res=Boolean(a); //output is false since 0 converts to false

var a=”splessons”;
var res=Boolean(a); //output is true since a has meaningful value

Trivial Datatype

shape Description

Trivial datatype is similar to primitive data type and contains two categories.

null type

Null type has only one special value null. Logically, null value is an empty object pointer, which returns “object” when passed.

var name=null; //name has no meaningful value assigned currently

alert(type of null);// “object”

When defining a variable that is meant to later hold an object, it is advisable to initialize the variable to null as opposed to anything else.

undefined type

Undefined type has only one special value undefined. When a variable is declared using var but not initialized, the value of undefined is as follows:

var a;
alert(a==undefined); //true

  • By default, any uninitialized variable gets the value of undefined.
  • Never explicitly set the value of a variable to undefined.
  • Undefined exists to differentiate between empty object/variable and uninitialized variable.

Composite Datatypes

shape Description

Composite Datatypes are important in JavaScript functioning and are also called as non-primitive datatypes. They are classified into 3 types, such as: All the three will be discussed in detail in further chapters.

Summary

shape Key Points

  • JavaScript DataTypes describe the type of data.
  • Primitive, Trivial and Composite are the different types of JavaScript DataTypes.
  • Numbers will be decimal, octal, hexadecimal and floating.
  • Null and undefined datatypes are almost the same.