Control Flow

Conditional Statements

Conditional statements execute different blocks of code depending on specified conditions.

if Statement

The if statement runs a block of code if a condition evaluates to true.

let age = 18;

if (age >= 18) {
  console.log("You are an adult.");
}

if...else Statement

The else block runs if the condition in if is false.

let age = 16;

if (age >= 18) {
  console.log("You are an adult.");
} else {
  console.log("You are a minor.");
}

if...else if...else Statement

Used when multiple conditions need to be checked.

let score = 85;

if (score >= 90) {
  console.log("Grade: A");
} else if (score >= 80) {
  console.log("Grade: B");
} else {
  console.log("Grade: C or lower");
}

Ternary Operator (Shorter if...else)

A shorthand way to write an if...else statement.

let isMember = true;
let discount = isMember ? "10% off" : "No discount";
console.log(discount);

Switch Statement

The switch statement is used when checking multiple possible values of a variable.

let day = "Monday";

switch (day) {
  case "Monday":
    console.log("Start of the week.");
    break;
  case "Friday":
      console.log("Weekend is near.");
      break;
  case "Sunday":
    console.log("Relax, it's the weekend.");
    break;
  default:
    console.log("A regular day.");
}

• break prevents fall-through execution to the next case.

• default runs if no case matches.

Loops in JavaScript

Loops allow repetitive execution of code until a condition is met.

for Loop

Used when the number of iterations is known.

for (let i = 1; i <= 5; i++) {
  console.log("Iteration:", i);
}

while Loop

Executes as long as the condition remains true.

let count = 1;

while (count <= 5) {
  console.log("Count:", count);
  count++;
}

do...while Loop

Similar to while, but always executes at least once.

let num = 1;

do {
  console.log("Number:", num);
  num++;
} while (num <= 3);

Loop Control Statements

break Statement

Exits a loop immediately.

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

Output: 1 2 3 4 (stops at 5).

continue Statement

Skips the current iteration and continues with the next.

for (let i = 1; i <= 5; i++) {
  if (i === 3) {
    continue;
  }
  console.log(i);
}

Output: 1 2 4 5 (skips 3).

Conclusion

This section covered conditional statements and loops, which control program flow. The next section will focus on functions, an essential part of writing reusable and structured JavaScript code.