Codnitional Branching

Range-based decisions utilize if-else ladders:

const temperature = 28;

if (temperature >= 30) {
    console.log("Hot weather: Use air conditioning");
} else if (temperature >= 20) {
    console.log("Mild weather: Open windows");
} else if (temperature >= 10) {
    console.log("Cool weather: Wear a jacket");
} else {
    console.log("Cold weather: Heating required");
}

Discrete value matching leverages switch statements with fall-through beahvior:

const grade = 'B';

switch (grade) {
    case 'A':
        console.log("Excellent performance");
        break;
    case 'B':
    case 'C':
        console.log("Satisfactory work");
        break;
    case 'D':
        console.log("Needs improvement");
        break;
    default:
        console.log("Invalid grade");
}

Iteration Constructs

The while loop evaluates conditions prior to execution:

let step = 1;
while (step <= 5) {
    console.log(`Processing step ${step}`);
    step++;
}

When guaranteed execution is requried, do-while ensures the block runs at least once:

let sumSquares = 0;
let val = 1;
do {
    sumSquares += val * val;
    val++;
} while (val <= 5);
console.log(sumSquares); // 55

The for loop consolidates counter management:

let product = 1;
for (let factor = 1; factor <= 5; factor++) {
    product *= factor;
}
console.log(product); // 120

Nested Loop Patterns

Generating tabular data requires nested iteration:

for (let row = 1; row <= 9; row++) {
    let lineOutput = '';
    for (let col = 1; col <= row; col++) {
        lineOutput += `${col}×${row}=${col * row}\t`;
    }
    console.log(lineOutput);
}