JavaScript Control Flow (While, Do-While, For & For-In Loop)

JavaScript Control Flow is similar to C, C++ or any programming language. Now the question is why we need JavaScript Control Flow or any other programming language, the reason is very simple as we all know that programs are groups of code and software are groups of programs so in a program there is a block of code we have to execute again and again and for saving space we can not write the code again and again to avoid this problem we use Control flow to control flow or block of code instead of writing again and again in a programming language.

In this tutorial, we will understand Control flow in detail with complete syntax and examples but before starting tutorials I just want to clear one doubt here in other programming languages we have only three JavaScript Control Flow (For Loop, Do…While Loop, and While Loop). We have one extra Control flow (For- in Loop), yes we have a total of four loops in javascript or we can say that four Control flow statements are in javascript. 

Basically, control flow controls the flow of programming and with the help of Loop avoid repetitive code. So in these tutorials, we are going to learn the JavaScript Control Flow Structures or For Loop control flow javascript or For-In Loop control flow javascript or While Loop control flow javascript or Do-While control flow javascript in-depth with the complete explanation.

JavaScript Control Flow– What Are We Going to Learn?

  1. Control Flow
  2. What is Loop
  3. Types of Loops
  4. For Loop
  5. For – in Loop
  6. While Loop
  7. Do-While Loop
  8. Syntax of Loops
  9. Examples of Loops

Note: I just want to clarify that there is a big difference between Control Flow and Conditional Statements tutorials in Javascript. If you don’t know about conditions statements I suggest you have to read the Conditional Statements in-depth article before reading this article. this will help you a lot to understand flow control flow in javascript.

1. Control Flow

When a block of code needs to be executed many times with a different value, Then Control statements are required, According to a satisfied condition. Basically, Loops are there to avoid repetitive code.

Control Flow

2. What are The Loops?

In computer programming, a loop is a sequence of instructions that is continually repeated until a certain condition is reached. Typically, a certain process is done, such as getting an item of data and changing it, and then some condition is checked such as whether a counter has reached a prescribed number or not.

Types of Loops or Loops in JavaScript

  1. For Loop
  2. For – in Loop
  3. While Loop
  4. Do-While Loop

1. For Loop

For loop is there to execute a block of code multiple times, For Loop is one of the best examples of a control flow of programs in programming statement in Javascript. Below is the syntax of FOR LOOP


for (statement 1; statement 2; statement 3) { code block }

Statement 1 is Checked or executed once before the execution.
Statement 2 Specify the condition of execution of code.
Statement 3 is executed every time until the specified condition is true.


for (i = 1; i <= 100; i++) { text += "Value of i is " + i + "<br>"; }

Here i=1 is statement1 which is executed once when execution of for loop will be started. Basically, we will use this to initialize that variable used by the loop.
I <=100 is statement 2 which is the basic condition that statements will be executed until the value of I will is 100.

i++ is statement three which is executed whenever control satisfies the defined condition and I will increment by 1 every time.

JavaScript Control Flow For Loop Example

<!DOCTYPE html> <html> <body> <h2>JavaScript Loops</h2> <p id="ForLoopdemo"></p> <script> var number = ""; var n; for (n = 0; n < 10; n++) { number += " Number is " + n + "<br>"; } document.getElementById("ForLoopdemo").innerHTML = number; </script> </body> </html>

We can omit these statements:

1.) Statement 1 Can be Omitted:

You can omit statement 1 as it is optional for us, You can write it like:


Initialize the variable before the loop started. var Total = 0; var i = 1; for ( ; i < = 100; i++) { Total = Total + i; } alert("Sum = " + Total);

2.) Statement 2 Can be Omitted:

As statement 2 is optional loop will work fine but you can put a break inside the for loop otherwise it will execute infinite times. Initialize the variable before the loop started.

var Total = 0; for (var i = 1 ; ; i++) { Total = Total + i; Break; } alert("Sum = " + Total);

3.) Statement 3 Can be Omitted:

  1. If you don’t write statement 3 but it can be incremented inside the for a loop.
  2. if you don’t define any of the increments or decrements in the variable it will be executed only once.
  3. Initialize the variable before the loop started.

var Total = 0; var i = 1; for ( ; i < = 100;) { Total = Total + i; i++; } alert("Sum = " + Total);

2. For-In Loop

the for..in the loop is executed object’s properties.

for (variablename in object) { code Block; }

here in For-In Loop each time one property of the object is assigned to the variable and the loop continues until the object’s properties are exhausted.


<!DOCTYPE html> <html> <body> <p id="ForIn"></p> <script> var book = {AuthorName:"Suman", bookName:"Tutorial", age:25}; var bookProperties = ""; var attributes; for (attributes in the book) { bookProperties += book[attributes] + " "; } document.getElementById("ForIn").innerHTML = bookProperties; </script> </body> </html>

3. While Loop

while the loop will execute the block of code until the condition we specified is true. When the control comes to condition and found that condition is false control comes out of the loop and execute the exact next statement after the while loop.

While Loop firstly checks the condition then statements are got executed.
while (var < lastvalue) { block of code; }


<html> <body> <script type="text/javascript"> var n=0 while (n<10) { document.write("Value of n is " + n) document.write("<br />") n=n+1 } </script> </body> </html>

Here loop will be executed 10 times, the value of the loop start for n=0 and the condition will be true till n=9. When n=10 then the condition will be false and control comes out of the While loop.

While Loop

4. Do…While Loop

The do…while loop, you can also say it a variant of a while. Here the block of code will be executed at least once before testing the condition. So even if the condition becomes false though the code will be executed once.

do { Block of code; } while (var<=lastValue)


<html> <body> <script type="text/javascript"> var n=0 do { document.write("value of n is " + n) document.write("<br />") n=n+1 } while (n<10) </script> </body> </html>

Tip: Always be careful when you use control flow in programming cause if your desired conditions are not matched then your control flow may be infinite or your loop can be endless. so always twice checks the conditions of Loops and you can fix the flow of a program using loops.

Author Bio

JavaScript Control Flow Tutorials is provided by Suman Yadav. Thanks, Suman for the Awesome and Unique article. If you want to submit your article and want to be a member of our Programming With Basics Family Join us by sending a well-written article more information read Write for Us
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Hi, I’m Ghanendra Yadav, SEO Expert, Professional Blogger, Programmer, and UI Developer. Get a Solution of More Than 500+ Programming Problems, and Practice All Programs in C, C++, and Java Languages. Get a Competitive Website Solution also Ie. Hackerrank Solutions and Geeksforgeeks Solutions. If You Are Interested to Learn a C Programming Language and You Don't Have Experience in Any Programming, You Should Start with a C Programming Language, Read: List of Format Specifiers in C.
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