JavaScript for Loop | JS for Loop

JavaScript for Loop | JS for Loop

In this tutorial, you will learn

  • Introduction JavaScript for Loop
  • Syntax of the for Loop
  • Flowchart of for loop
  • JavaScript for loop examples
    • Example 1: Print number from 1 to 5 using for loop
    • Example 2: The for loop without the initialization part example
    • Example 3: Sum of 1 to n numbers using for loop in javascript
    • Example 4: Find average of n numbers using for loop in JavaScript

Introduction JavaScript for Loop

The JavaScript for loop is also known as an entry control loop. The JavaScript for is test specified condition before executing a block of code. If the condition met true, then block of code will be executed.

Note:- It’s the concise form of loop.

Syntax of the for Loop

for (initialization; condition; post-expression) {
     // statements
 }

Here,

1) initialization

The initialization expression initializes the loop. The initialization expression is executed only once when the loop starts.

2) condition

The condition is check once before every iteration. The block of codeinside the loop is executed only when the condition is met true. If the condition metfalse. The execution of loop will be stopped.

3) post-expression

The for loop statement also evaluates the post-expression after each loop iteration. Generally, update post-expression(increment/decrement).

Flowchart of for loop

Flowchart of for loop

JavaScript for loop examples

Let’s take some examples of using the for loop.

Example 1: Print number from 1 to 5 using for loop

The following example uses the javascript for loop statement that print the numbers from 1 to 5.

<script>

    for (var count = 1; count <= 5; count++) 
    {
        document.write(count + "<br>")
    }

</script> 

The output of the script shown below:

1
2
3
4
5

How it works:

  • First, declare a variable  count and initialize it to 1.
  • Next, print the value of count.
  • Increase the value of countby 1 in each iteration of the loop.

Example 2: The for loop without the initialization part example

The following example uses a for loop that omits the initialization part:

<script>

    var j = 1;
    for (; j < 10; j += 2) 
    {
        document.write(j + "<br>")
    }

</script>  

The output of the script shown below:

1
3
5
7
9

Example 3: Sum of 1 to n numbers using for loop in javascript

The following example uses the javascript for loop statement that sum of 1 to n the numbers.

<script>

   let sum = 0;
   let n = 5;
   for(let i = 1; i <= n; i++) 
   {
    sum = sum + i;
   }
   document.write("Sum of 1 to n number is " + sum+ "<br>")


</script>  

The output of the script shown below:

Sum of 1 to n number is 15

How it works:

  • First, declare a variables  sum and n and initialize.
  • Next, specified test condition.
  • Increase the value of countby 1 in each iteration of the loop.
  • Using the this formula sum = sum + i;, calculate sum of n number.
  • Outside the for loop, Print sum variable.

Example 4: Find average of n numbers using for loop in JavaScript

The following example uses the javascript program to find sum of n numbers:

<script>

   let sum = 0;
   let n = 5;
   for(let i = 1; i <= n; i++) 
   {
    sum = sum + i;
   }
   
   avg = sum/n;

   document.write("Average of 1 to n number is " + avg + "<br>")

</script> 

The output of the script shown below:

Average of 1 to n number is 3

How it works:

  • First, declare a variables  sum and n and initialize.
  • Next, specified test condition.
  • Increase the value of countby 1 in each iteration of the loop.
  • Using the this formula sum = sum + i, to calculate sum of n number.
  • Outside the loop, use this formula avg = sum/n, to calculate the average of n numbers.
  • Outside the for loop, Print avg variable.

Conclusion

In this tutorial, you have learned what is for loop and how to use the JavaScript for loop statements with various examples.

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