JavaScript Conditionals

if Statement

Basic Structure

if (condition) {
    // code block
}

Example

Output:

Runs the block if the condition is true.

if-else Statement

Executes one block of code if a condition is true, and another block if it is false.

let age = 17;

if (age >= 18) {
  console.log("Adult");
} else {
  console.log("Minor");
}

else if Statement

Allows you to check multiple conditions in sequence, executing the first block whose condition is true.

let grade = 75;

if (grade >= 90) {
  console.log("A");
} else if (grade >= 80) {
  console.log("B");
} else if (grade >= 70) {
  console.log("C");
} else {
  console.log("Fail");
}

Nested if Statements

Used when a decision depends on multiple conditions.

let temperature = 25;

if (temperature > 0) {
  if (temperature < 30) {
    console.log("Nice weather");
  }
}

switch Statement

let fruit = "apple";

switch (fruit) {
  case "banana":
    console.log("Yellow");
    break;
  case "apple":
    console.log("Red or Green");
    break;
  case "orange":
    console.log("Orange");
    break;
  default:
    console.log("Unknown fruit");
}

Truthy and Falsy

if (0) console.log("No");       // Not executed
if ("hello") console.log("Yes"); // Executed

Falsy values: 0, "", null, undefined, NaN, false

Best Practices

Use {} even for single-line blocks to prevent bugs
Prefer switch for multiple discrete values
Understand truthy/falsy behavior for safer logic

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