Logic Statements

Logic statements allow a program to choose between different execution paths based on conditions.

A condition evaluates to true or false.
A branch executes only when its condition is satisfied.
Logic statements implement control flow.

[Condition?] | True False | | if block else block

🔵 2

if and if...else

Basic if

let temperature = 30;
if (temperature > 25){
    console.log("It is warm outside.");
}

›It is warm outside.

if...else

let isLoggedIn = false;
if(isLoggedIn){
   console.log("Welcome back!");
}else{
   console.log("Please log in first.");
}

›Please log in first.

🟣 3

else if Chain

let score=78;
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 D");
}

›Grade C

Conditions are checked from top to bottom. The first true condition executes. Here score = 78 fails >=90 and >=80, but satisfies >=70, so "Grade C" is logged.

🟢 4

Truthy and Falsy

Falsy values: false, 0, -0, "" (empty string), null, undefined, NaN

let name="";
if(name){
 console.log("Name is provided");
}else{
 console.log("Name is missing");
}

›Name is missing

🟠 5

Comparison and Logical Operators

Operator	Meaning
`==`	Equal (coercion)
`===`	Strict Equal
`!=`	Not Equal
`!==`	Strict Not Equal
`>`	Greater Than
`<`	Less Than
`>=`	Greater Than or Equal
`<=`	Less Than or Equal

Logical Operators: && — AND · || — OR · ! — NOT

let age=20;
let hasID=true;
if(age>=18 && hasID){
 console.log("Access granted");
}

›Access granted

let isAdmin=false;
let isModerator=true;
if(isAdmin || isModerator){
 console.log("You can manage comments.");
}

›You can manage comments.

let isComplete=false;
if(!isComplete){
 console.log("Task is not complete yet.");
}

›Task is not complete yet.

🩷 6

Conditional (Ternary) Operator

let age=17;
let message=(age>=18)?"Adult":"Minor";
console.log(message);

›Minor

The ternary operator is a concise alternative to simple if...else statements: condition ? valueIfTrue : valueIfFalse.

🔷 7

switch Statement

let day="Wednesday";
switch(day){
 case "Monday":
   console.log("Start of week");
   break;
 case "Wednesday":
   console.log("Middle of week");
   break;
 default:
   console.log("Another day");
}

›Middle of week

🚫 Without break, execution falls through to the next case even if its condition doesn't match — always terminate each case with break unless fall-through is intentional.

⚪ 8

Choosing Between if and switch

Use if...else for ranges and inequalities. Use switch for matching a single variable against multiple exact values.

🔴 9

Complete Example — Movie Ticket Price Calculator

let age=16;
let isStudent=true;
let dayOfWeek="Wednesday";
let basePrice;
if(age<12){
 basePrice=5;
}else if(age<18){
 basePrice=8;
}else{
 basePrice=10;
}
let discount=isStudent?2:0;
let finalPrice;
switch(dayOfWeek){
 case "Wednesday":
   finalPrice=basePrice-discount-1;
   break;
 default:
   finalPrice=basePrice-discount;
}
console.log(finalPrice);

›5

Trace: age=16 fails <12 but satisfies <18, so basePrice=8. isStudent is true, so discount=2. dayOfWeek is "Wednesday", so finalPrice = 8 - 2 - 1 = 5.

📋 Summary

Chapter Summary

if
if...else
else if
Truthy & Falsy
Comparison Operators
Logical Operators
Ternary Operator
Switch Statement
Fall-through
Choosing between if and switch