JavaScript Loops

Different Kinds of Loops

JavaScript supports different kinds of loops:

• for - loops through a block of code a number of times
• for/in - loops through the properties of an object
• while - loops through a block of code while a specified condition is true
• do/while - also loops through a block of code while a specified condition is true

The For Loop

The for loop is often the tool you will use when you want to create a loop.

The for loop has the following syntax:

for (statement 1; statement 2; statement 3)   {   the code block to be executed   }

Statement 1 is executed before the loop (the code block)  starts.

Statement 2 defines the condition for running the loop (the code block).

Statement 3 is executed each time after the loop (the code block) has been executed.

The For/In Loop

The JavaScript for/in statement loops through the properties of an object:

Example

var person={fname:"John",lname:"Doe",age:25}; 

 for (x in person)
   {
   txt=txt + person[x];
   }

The While Loop

The while loop loops through a block of code as long as a specified condition is true.

Syntax

while (condition)
   {
  code block to be executed
   }

The Do/While Loop

The do/while loop is a variant of the while loop. This loop will  execute the code block once, before checking if the condition is true, then it will repeat the loop as long as the condition is true.

Syntax

do
   {
  code block to be executed
   }
 while (condition);