JavaScript Conditions

What is a condition?

A condition is an expression used to make a decision. JavaScript evaluates the expression in a boolean context and then chooses which block of code to execute.

const score = 75;

if (score >= 40) {
  console.log("Pass");
}

The if statement

if runs a block only when its condition is truthy.

const isLoggedIn = true;

if (isLoggedIn) {
  console.log("Welcome back");
}

Parentheses contain the condition and curly braces contain the code block.

if...else

Use else when you need an alternative path if the if condition is false.

const age = 16;

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

else if chains

Use else if when multiple mutually exclusive conditions need to be checked in order.

const score = 82;

if (score >= 90) {
  console.log("Grade A+");
} else if (score >= 75) {
  console.log("Grade A");
} else if (score >= 60) {
  console.log("Grade B");
} else if (score >= 40) {
  console.log("Pass");
} else {
  console.log("Try again");
}

Conditions with comparison operators

Comparison operators from Chapter 4 are commonly used inside conditions.

const temperature = 31;

if (temperature > 30) {
  console.log("Hot day");
}

if (temperature === 31) {
  console.log("Exactly 31 degrees");
}

Prefer strict equality === when comparing values unless coercion is explicitly intended.

Combining conditions

Logical operators let you combine multiple checks.

const isLoggedIn = true;
const hasSubscription = true;

if (isLoggedIn && hasSubscription) {
  console.log("Open course");
}

const role = "editor";

if (role === "admin" || role === "editor") {
  console.log("Editing allowed");
}

• && requires both sides to be truthy.
• || needs at least one truthy side.
• ! reverses truthiness.

Checking numeric ranges

JavaScript does not support mathematical chained comparisons such as 18 <= age <= 60. Write each comparison explicitly.

const age = 25;

if (age >= 18 && age <= 60) {
  console.log("Within range");
}

Truthy and falsy in conditions

An if condition does not require a literal boolean. JavaScript converts the tested value to boolean truthiness.

const userName = "Broun";

if (userName) {
  console.log("Name is available");
}

const message = "";

if (!message) {
  console.log("Message is empty");
}

Common falsy values include false, 0, empty string, null, undefined and NaN.

Explicit checks can be clearer

Truthy checks are concise, but explicit comparisons can communicate intent better when values such as 0 or an empty string are valid data.

const cartCount = 0;

if (cartCount === 0) {
  console.log("Cart is empty");
}

Nested conditions

An if block can contain another condition, but too much nesting makes code harder to read.

const isLoggedIn = true;
const role = "student";

if (isLoggedIn) {
  if (role === "student") {
    console.log("Open student dashboard");
  }
}

The switch statement

switch is useful when one value is compared against several exact cases.

const day = "monday";

switch (day) {
  case "monday":
    console.log("Start the week");
    break;
  case "friday":
    console.log("Almost weekend");
    break;
  default:
    console.log("Regular day");
}

switch matching uses strict comparison behavior. The default branch runs when no case matches.

Why break matters in switch

Without break, execution can continue into following cases. This is called fall-through.

const level = 1;

switch (level) {
  case 1:
    console.log("Beginner");
    break;
  case 2:
    console.log("Intermediate");
    break;
  default:
    console.log("Unknown level");
}

Grouping switch cases

Multiple cases can intentionally share the same block.

const role = "editor";

switch (role) {
  case "admin":
  case "editor":
    console.log("Can edit content");
    break;
  default:
    console.log("Read only");
}

Ternary operator

The conditional or ternary operator is a compact expression for choosing between two values.

const score = 75;
const result = score >= 40 ? "Pass" : "Fail";

console.log(result);

Syntax: condition ? valueIfTrue : valueIfFalse.

if...else vs switch vs ternary

• Use if...else for ranges, multiple expressions and flexible conditions.
• Use switch when one value is matched against several exact cases.
• Use ternary for a short two-way value choice.

Practical access check

const isLoggedIn = true;
const progress = 80;

if (!isLoggedIn) {
  console.log("Please sign in");
} else if (progress === 100) {
  console.log("Course complete");
} else if (progress >= 75) {
  console.log("Almost complete");
} else {
  console.log("Keep learning");
}

Beginner best practices

• Conditions ko short and readable rakho.
• Equality ke liye generally === and !== prefer karo.
• Complex boolean logic me parentheses use karo when it improves clarity.
• Range checks ko separate comparisons with && me likho.
• switch me accidental fall-through avoid karo.
• Nested ternaries avoid karo.
• Real values such as 0 ko falsy shortcut se accidentally reject mat karo.

Common beginner mistakes

• = ko condition me equality operator samajhna.
• == aur === difference ignore karna.
• else if conditions wrong order me rakhna.
• 18 <= age <= 60 jaisi mathematical chaining likhna.
• switch cases me break bhoolna.
• Boolean logic ko unnecessarily deeply nest karna.
• Complex nested ternary expressions banana.
• Truthy/falsy behavior samjhe bina shortcuts use karna.

Chapter checklist

• if, else and else if use kar sakte ho?
• Logical operators ke saath conditions combine kar sakte ho?
• Truthy/falsy values condition me kaise behave karti hain clear hai?
• Numeric range correctly check kar sakte ho?
• switch, case, break and default samajh aaye?
• Ternary operator kab appropriate hai clear hai?