JavaScript Control Flow: Conditions and Loops

Conditional Statements

if / else if / else

const score = 75;

if (score >= 90) {
    console.log("Grade A");
} else if (score >= 75) {
    console.log("Grade B");
} else if (score >= 60) {
    console.log("Grade C");
} else {
    console.log("Fail");
}
// Output: Grade B

Ternary Operator

const age = 20;
const status = age >= 18 ? "Adult" : "Minor";
console.log(status); // Adult

Switch Statement

const day = "Monday";

switch (day) {
    case "Monday":
    case "Tuesday":
        console.log("Weekday");
        break;
    case "Saturday":
    case "Sunday":
        console.log("Weekend");
        break;
    default:
        console.log("Midweek");
}

Loops

for Loop

for (let i = 0; i < 5; i++) {
    console.log(i);  // 0 1 2 3 4
}

// Reverse
for (let i = 5; i > 0; i--) {
    console.log(i);  // 5 4 3 2 1
}

while Loop

let count = 0;
while (count < 3) {
    console.log("Count: " + count);
    count++;
}

do...while Loop

let n = 0;
do {
    console.log(n);
    n++;
} while (n < 3);
// Executes at least once

for...of (Arrays)

const fruits = ["apple", "banana", "cherry"];
for (const fruit of fruits) {
    console.log(fruit);
}

for...in (Objects)

const person = { name: "Alice", age: 25, city: "Delhi" };
for (const key in person) {
    console.log(`${key}: ${person[key]}`);
}

Loop Control

for (let i = 0; i < 10; i++) {
    if (i === 3) continue; // Skip 3
    if (i === 7) break;    // Stop at 7
    console.log(i);        // 0 1 2 4 5 6
}

Loop Comparison

Key Takeaway: JavaScript has rich control flow. Use === in conditions, prefer for...of for arrays, and for...in for objects. Use break and continue to control loop execution.