Control Flow

Control Flow in JavaScript

What Is Control Flow?

Control flow determines the order in which code is executed. It lets you make decisions or repeat code using:

1. Conditional statements (if, else, switch)
2. Loops (for, while, do...while)
3. Control keywords (break, continue, return)

---

1. Conditional Statements

if, else if, else

Run code only when a condition is true.

let age = 20;

if (age >= 18) {
  console.log("You are an adult.");
} else if (age >= 13) {
  console.log("You are a teenager.");
} else {
  console.log("You are a child.");
}

---

switch Statement

Compare a variable to multiple exact values.

let fruit = "apple";

switch (fruit) {
  case "apple":
    console.log("You chose apple.");
    break;
  case "banana":
    console.log("You chose banana.");
    break;
  default:
    console.log("Unknown fruit.");
}

Use break to prevent fall-through to the next case.

---

2. Loops

for Loop

Run code a fixed number of times.

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

---

while Loop

Repeat while a condition is true.

let i = 0;
while (i < 5) {
  console.log("i is", i);
  i++;
}

---

do...while Loop

Runs at least once before checking the condition.

let i = 0;
do {
  console.log("Number is", i);
  i++;
} while (i < 5);

---

3. Control Keywords

break: Exit a loop or switch early

for (let i = 0; i < 10; i++) {
  if (i === 5) break;
  console.log(i);
}

continue: Skip the current loop iteration

for (let i = 0; i < 5; i++) {
  if (i === 2) continue;
  console.log(i);
}

If there is a loop in loop, we can use a label to break or continue specific loop

outer: for (let i = 0; i < 3; i++) {
  for (let j = 0; j < 3; j++) {
    console.log(`i=${i}, j=${j}`);
    if (i === 1 && j === 1) {
      break outer; // breaks the outer loop 
    }
  }
}

return: Exit a function and return a value

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✅ Summary

Keyword	Use For
if / else	Run code based on a condition
switch	Match a value to many options
for	Loop a known number of times
while	Loop with a condition
do...while	Like while, but runs once first
break	Exit a loop or switch early
continue	Skip this loop step
return	Exit a function