Control Flow

Introduction

Control flow determines how your program executes step by step.

Instead of running line by line blindly, JavaScript uses conditions and loops to:

Make decisions
Repeat tasks
Control execution paths

Control Flow Overview

graph TD A[Start] --> B{Condition} B -->|True| C[Execute Block A] B -->|False| D[Execute Block B] C --> E[End] D --> E

Conditional Statements

if, else if, else

Used to execute code based on conditions.

let score = 75;

if (score >= 90) {
    console.log("A");
} else if (score >= 70) {
    console.log("B");
} else {
    console.log("C");
}

Flow Diagram

graph TD A[Condition] -->|True| B[Run if block] A -->|False| C[Run else block]

Ternary Operator

Short form of if-else.

let result = age >= 18 ? "Adult" : "Minor";

Logical Flow

graph TD A[Condition 1] --> B{AND / OR} C[Condition 2] --> B B --> D[Result]

switch Statement

Used when checking multiple fixed values.

let day = 2;

switch (day) {
    case 1:
        console.log("Monday");
        break;
    case 2:
        console.log("Tuesday");
        break;
    default:
        console.log("Other day");
}

Loops in JavaScript

Loops are used to repeat tasks efficiently.

Loop Overview

graph TD A[Start] --> B{Condition} B -->|True| C[Execute Body] C --> B B -->|False| D[End]

for Loop

Best when number of iterations is known.

for (let i = 0; i < 5; i++) {
    console.log(i);
}

while Loop

Runs while condition is true.

let i = 0;

while (i < 5) {
    console.log(i);
    i++;
}

do…while Loop

Runs at least once.

let i = 0;

do {
    console.log(i);
    i++;
} while (i < 5);

for…in Loop

Used for iterating object keys.

let user = { name: "Sahil", age: 20 };

for (let key in user) {
    console.log(key, user[key]);
}

for…of Loop

Used for iterating iterables (arrays, strings).

let arr = [10, 20, 30];

for (let value of arr) {
    console.log(value);
}

forEach Method

Array method for iteration.

let arr = [1, 2, 3];

arr.forEach((value, index) => {
    console.log(value, index);
});

Loop Comparison

for

Use when iteration count is known.

while

Use when condition-based looping.

do...while

Use when loop must run at least once.

for...in

Use for objects (keys).

for...of

Use for arrays and iterables (values).

forEach

Use for clean array iteration (no break).

break and continue

for (let i = 0; i < 5; i++) {
    if (i === 2) continue;
    if (i === 4) break;

    console.log(i);
}

break → exits loop
continue → skips iteration