JavaScript For Loop

By | February 16, 2021
JavaScript For Loop

For loop is one of the most common looping structures provided by all the high-level programming languages. In the previous JavaScript tutorial, we discuss how can we use while and do..while loop in JavaScript to execute a block of code repeatedly, in this tutorial we will learn about the JavaScriptfor loop.

JavaScript for loop Statement

Similar to the JavaScript while loop, we can use the for loop to execute a block of code repeatedly until the condition becomes false. But unlike the while loop the for loop is generally used when we are certain about the number of times we want to execute the code block.

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JavaScript for loop Syntax

To implement the for loop in JavaScript we use the following syntax

for(initialization exresssion; condition expression;  increment/decrement expression )
   {
      //for loop code block
   }

In the syntax, you can see that for loop statement comprise three expressions

  • initialization expression
  • condition expression
  • increment/decrement expression

And all these three expressions are separated with semicolons ; and inside the bracket ().

In the initialization expression, we use the assignment statement and set a starting value to the counter variable.

In the condition expression, we set a conditional statement for the true or false value. If the value is true the for loop code block will execute, otherwise, we will get out of the loop. Generally, the conditional expression specifies the endpoint for the counter variable.

In the Increment/Decrement expression, we increase or decrease the value of the counter variable. If the initialization counter value is greater than the condition value, there we use the decrement operator, if the counter variable initial value is less than the conditional value then we use the increment operator.

for loop Flow Chart

Example

<!DOCTYPE html>
<html>
    <head>
        <title></title>
        <script>
            document.write("<h3> JavaScript For Example</h3>");

            for(let counter =0 ; counter<=10; counter++)
            {
                document.write(counter)
                document.write("<br/>") //new line
            } 
        </script>
    <body>       
    </body>
</html>

Output

Behind the code 

In the above for loop example

Initialization expression was let counter =0, which set the initial value of the counter to 0.

conditions expression was counter<=10, and, that will become false when the counter value becomes 11.

increment/decrement expression was counter++, which increase the value of the counter by 1 with each iteration.

When you use all the three expressions inside the for() loop be careful with the condition and increment/decrement expressions because if the increment/decrement expression does not set the condition to false after a specific set of iteration, then the loop will fall into infinity.

Summary

  • for loop is used to execute a block of code up to a certain number of times.
  • It contains 3 expressions, initialization, condition, and increment/decrement.

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