# Control Flow in JavaScript: If, Else, and Switch Explained

Every single day, we make decisions. If it's raining, we carry an umbrella. If the chai is too hot, we wait. If it's a holiday, we sleep in. We are constantly checking conditions and choosing what to do based on the result.

Our code works the same way. Control flow is just the order in which our program makes decisions and executes code. And the tools JavaScript gives us for that are `if`, `else`, and `switch`.

* * *

## The if Statement

The `if` statement is the simplest form of decision making in JavaScript. It says: if this condition is true, run this block of code.

```javascript
let marks = 75;

if (marks >= 50) {
  console.log("Passed!");
}
// Output: Passed!
```

JavaScript checks the condition inside the parentheses. If it evaluates to `true`, the code inside the curly braces runs. If it is `false`, JavaScript skips that block entirely and moves on.

* * *

## The if-else Statement

What if we want something to happen when the condition is false as well? That is where `else` comes in.

```javascript
let marks = 35;

if (marks >= 50) {
  console.log("Passed!");
} else {
  console.log("Failed. Try again.");
}
// Output: Failed. Try again.
```

Think of it like this. We are at a gate. If we have a ticket, we get in. If we do not have a ticket, we are turned away. One condition, two possible outcomes.

* * *

## The else if Ladder

Sometimes two options are not enough. What if we want to check multiple conditions one after another? We use `else if` to build a ladder.

```javascript
let marks = 72;

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

JavaScript goes through each condition from top to bottom. The moment it finds one that is true, it runs that block and skips everything else. If none of the conditions match, the final `else` acts as the fallback.

* * *

## The switch Statement

Now imagine we have one variable and we want to check it against many specific values. We could write a long `else if`ladder, but there is a cleaner way for situations like this.

```javascript
let day = 3;

switch (day) {
  case 1:
    console.log("Monday");
    break;
  case 2:
    console.log("Tuesday");
    break;
  case 3:
    console.log("Wednesday");
    break;
  case 4:
    console.log("Thursday");
    break;
  default:
    console.log("Another day");
}
// Output: Wednesday
```

The `switch` statement takes a value and compares it against each `case`. When it finds a match, it runs that block of code.

Now notice the `break` keyword after each case. That is important. Without `break`, JavaScript does not stop after finding a match. It keeps running every case below it until it hits the end of the switch block. That behaviour is called fall-through and it causes bugs if we are not careful.

The `default` at the bottom is like the `else` in an if-else chain. It runs when none of the cases match.

* * *

## When to Use switch vs if-else

Both do the job of decision making, but they suit different situations.

`if-else` is more flexible. We can check ranges, compare two different variables, or write any kind of condition inside it. When the logic is complex or the conditions are not simple equality checks, `if-else` is the right pick.

```javascript
let age = 20;
let hasID = true;

if (age >= 18 && hasID) {
  console.log("Entry allowed");
} else {
  console.log("Entry not allowed");
}
```

`switch` works best when we are comparing one variable against a list of fixed, specific values. It reads more cleanly in those situations and is easier to scan through.

```javascript
let plan = "pro";

switch (plan) {
  case "free":
    console.log("You have 5GB storage");
    break;
  case "basic":
    console.log("You have 20GB storage");
    break;
  case "pro":
    console.log("You have 100GB storage");
    break;
  default:
    console.log("Unknown plan");
}
// Output: You have 100GB storage
```

A simple way to decide: if the condition is about checking a range or combining multiple variables, go with `if-else`. If we are checking one variable against a bunch of specific values, `switch` keeps things neat.

* * *