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.

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

Output

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

For loop to print table of a number

let x = 5;
for (let i = 1; i <= 10; i++) {
  console.log(x * i); 
}

Output

5
10
15
20
25
30
35
40
45
50

For loop to print elements of an array

let arr = [10, 20, 30, 40];
for (let i = 0; i < arr.length; i++) {
  console.log(arr[i]); 
}

Output

10
20
30
40

Syntax of 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: Initialization of the counter (executed once before the loop starts).
• Statement 2: Condition check before each iteration.
• Statement 3: Increment or decrement of the counter (executed after each loop iteration).

Statement 1: Initializing Counter Variable

Statement 1 initializes the counter variable. This variable tracks the number of iterations. It can be initialized inside or outside the loop.

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 condition before each iteration. If true, the loop executes; otherwise, it stops. If omitted, the loop runs indefinitely unless manually stopped.

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

Output

Value of x:2

Statement 3: Updating Counter Variable

This statement updates the counter variable. It is optional and can be placed inside the loop body instead.

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

Output

MathsSciencePolityHistory

More Loops in JavaScript

JavaScript offers different types of loops:

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