JavaScript For Loop

JavaScript for loop is a control flow statement that allows code to be executed repeatedly based on a condition. It consists of three parts: initialization, condition, and increment/decrement. This loop iterates over a code block until the specified condition is false.

For Loop in JavaScript

A for loop in JavaScript repeatedly executes a block of code as long as a specified condition is true. It includes initialization, condition checking, and iteration steps, making it efficient for controlled, repetitive tasks.

Syntax:

for (statement 1 ; statement 2 ; statement 3){
    code here...
}

• Statement 1: It is the initialization of the counter. It is executed once before the execution of the code block.
• Statement 2: It defines the testing condition for executing the code block
• Statement 3: It is the increment or decrement of the counter & executed (every time) after the code block has been executed.

Example:

// JavaScript program to illustrate for loop
let x;

// for loop begins when x=2
// and runs till x <=4
for (x = 2; x <= 4; x++) {
    console.log("Value of x:" + x);
}

Output:

Value of x:2
Value of x:3
Value of x:4

Flow chart

This flowchart shows the working of the for loop in JavaScript. You can see the control flow in the For loop.

Statement 1: Initializing Counter Variable

Statement 1 is used to initialize the counter variable. A counter variable is used to keep track of the number of iterations in the loop. You can initialize multiple counter variables in statement 1.

We can initialize the counter variable externally rather than in statement 1. This shows us clearly that statement 1 is optional. We can leave the portion empty with a semicolon. 

Example:

let x = 2;

for (; x <= 4; x++) {
    console.log("Value of x:" + x);
}

Output

Value of x:2
Value of x:3 
Value of x:4

Statement 2: Testing Condition

This statement checks the boolean value of the testing condition. If the testing condition is true, the for loop will execute further, otherwise loop will end and the code outside the loop will be executed. It is executed every time the for loop runs before the loop enters its body.

This is also an optional statement and Javascript treats it as true if left blank. If this statement is omitted, the loop runs indefinitely if the loop control isn’t broken using the break statement. It is explained below in the example.

Example:

let x = 2;
for (; ; x++) {
    console.log("Value of x:" + x);
    break;
}

Output:

Value of x:2

Statement 3: Updating Counter Variable

It is a controlled statement that controls the increment/decrement of the counter variable.

It is also optional by nature and can be done inside the loop body.

Example:

const subjects = ["Maths", "Science", "Polity", "History"];
let i = 0;
let len = subjects.length;
let gfg = "";
for (; i < len;) {
    gfg += subjects[i];
    //can be increased inside loop
    i++;
}
console.log(gfg)

Output

MathsSciencePolityHistory

More Loops in JavaScript

JavaScript has different kinds of loops in Java. Some of the loops are:

Learn and master JavaScript with Practice Questions. JavaScript Exercises provides many JavaScript Exercise questions to practice and test your JavaScript skills.

JavaScript For Loop – FAQs

What is a for loop in JavaScript?

A for loop is a control flow statement that allows code to be executed repeatedly based on a given Boolean condition. It is often used when the number of iterations is known beforehand.

What is the basic syntax of a for loop?

The basic syntax of a for loop consists of three parts: initialization, condition, and increment/decrement.

Example: for (initialization; condition; increment/decrement) { // code to be executed }

How does the initialization part work?

The initialization part is executed only once before the loop starts. It is typically used to initialize a counter variable.

Example: for (let i = 0; i < 5; i++) { console.log(i); } Here, let i = 0 is the initialization.

What is the purpose of the condition part?

The condition part is evaluated before each iteration of the loop. If the condition evaluates to true, the loop body is executed. If it evaluates to false, the loop terminates.

Example: for (let i = 0; i < 5; i++) { console.log(i); } Here, i < 5 is the condition.

How does the increment/decrement part work?

The increment/decrement part is executed after each iteration of the loop. It is typically used to update the loop counter variable.

A

ashishsaini3

Follow

Improve