Conditionals in JavaScript

What Are Conditionals?

Conditionals let your code make decisions. They execute different blocks of code based on whether a condition is true or false.

The if Statement

The most basic conditional. If the condition is true, the code runs.

let age = 18;

if (age >= 18) {
  console.log("You can vote!");
}

if/else — Two Paths

One path for when the condition is true, another for when it's false.

let temperature = 25;

if (temperature > 30) {
  console.log("It's hot outside.");
} else {
  console.log("It's pleasant outside.");
}

else if — Multiple Conditions

Check multiple conditions in sequence.

let score = 85;

if (score >= 90) {
  console.log("Grade: A");
} else if (score >= 80) {
  console.log("Grade: B");
} else if (score >= 70) {
  console.log("Grade: C");
} else {
  console.log("Grade: F");
}

The Ternary Operator (?)

A shorthand for if/else when you have a simple condition.

let age = 20;
let status = age >= 18 ? "Adult" : "Minor";
console.log(status); // "Adult"

switch Statements

Useful when you're comparing the same value against many possibilities.

let day = "Monday";

switch (day) {
  case "Monday":
    console.log("Start of the work week");
    break;
  case "Friday":
    console.log("TGIF!");
    break;
  case "Saturday":
  case "Sunday":
    console.log("Weekend!");
    break;
  default:
    console.log("Midweek");
}

Truthy and Falsy Values

In JavaScript, conditions don't have to be strictly true or false. Some values are "truthy" and some are "falsy".

• Falsy: false, 0, "" (empty string), null, undefined, NaN
• Truthy: Everything else — true, "hello", 42, [], {}

Common Mistakes

• Using = (assignment) instead of === (comparison) in conditions
• Forgetting to use break in switch statements
• Overcomplicating simple conditions — use the ternary operator for concise code

Quick Quiz

Summary

• if runs code when a condition is true
• if/else provides two paths
• else if allows multiple conditions
• The ternary operator (?) is a shorthand for simple if/else
• switch is useful for many comparisons of the same value
• Remember falsy values: false, 0, "", null, undefined, NaN