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If Statements in JavaScript

JavaScript if…else Statements

While writing a program, there may be a situation when you need to adopt one path out of the given two paths. So you need to make use of conditional statements that allow your program to make correct decision and perform right actions.

JavaScript supports conditional statements which are used to perform different actions based on different conditions. Here we will explain if… else statement

JavaScript supports following forms of if…else statement:

  • if statement
  • if… else statement
  • if….. else if….. statement

 

If statement

The if statement if the fundamental control statement that allows JavaScript to make decision and execute statements conditionally.

Syntax

if(expression){

statement(s) to be executed if expression is true

}

Here JavaScript expression is evaluated. If the resulting value is true, given statement(s) are executed. If expression is false then no statement would be not executed. Most of the times you will use comparison while making decisions

 

Example

<script type=”text/javascript”>

<!—

var age=20;

if(age>18)

{

document.write(“<b>Qualifies for driving </b>”);

}

//– >

</script>

This will produce following result :

Qualifies for driving

 

if….else statement

The if…else statement is the next form of control statement that allows JavaScript to execute statements in more controlled way.

Syntax

if  (expression)

{

statement(s) to be executed if expression is true

} else {

statement(s) to be executed if expression is false

}

Here JavaScript expression is evaluated, if the resulting value is true, given statement(s) in the if block, are executed. If expression is false then given stement(s) in the else block, are executed.

 

Example

<script   type=”text/javascript”>

<!—

var age= 15;

if(age>18)

{

document.write(“<b> Qualifies for dividing</b>”);

}

else

{

document.wirte(“<b> Does not qualify for driving </b>”);

}

//- – >

</script>

This will produce following result

 

Does not qualify for driving

if…else if … statement

The if…. else if… statement is the one level advance form of control statement that allows JavaScript to make correct decision out of several conditions.

 

Syntax

If  (expression 1) {

statement(s) to be executed if expression 1 is true

} else if (expression 2) {

statement(s) to be executed if expression 2 is true

} else if (expression 3){

Statement(s) to be executed if expression 3 is true

} else {

Statement(s) to be executed if no expression is true

}

There is nothing special about this code. It is just a series of if statements, where each if is part of the else clause of the previous statement. Statement(s) are executed based on the true condition, if none of the condition is true then else block executed.

 

Example 

<script type=”text/javascript”>

<!—

var book=”maths”;

if(book == “history”)

{

document.wirte(“<b>History Book</b>”);

}

else if(book== “economics”)

{

document.write(“<b>Economics Book</b>”);

} else {

document.write(“<b>Unknown  Book</b>”);

}

// – – >

</script>

This will produce following result:

Maths Book

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If Statements in JavaScript
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