Conditional statements execute different blocks of code depending on specified conditions.
The if statement runs a block of code if a condition evaluates to true.
let age = 18;
if (age >= 18) {
console.log("You are an adult.");
}let age = 18;
if (age >= 18) {
console.log("You are an adult.");
}let age = 18;
if (age >= 18) {
console.log("You are an adult.");
}The else block runs if the condition in if is false.
let age = 16;
if (age >= 18) {
console.log("You are an adult.");
} else {
console.log("You are a minor.");
}let age = 16;
if (age >= 18) {
console.log("You are an adult.");
} else {
console.log("You are a minor.");
}let age = 16;
if (age >= 18) {
console.log("You are an adult.");
} else {
console.log("You are a minor.");
}Used when multiple conditions need to be checked.
let score = 85;
if (score >= 90) {
console.log("Grade: A");
} else if (score >= 80) {
console.log("Grade: B");
} else {
console.log("Grade: C or lower");
}let score = 85;
if (score >= 90) {
console.log("Grade: A");
} else if (score >= 80) {
console.log("Grade: B");
} else {
console.log("Grade: C or lower");
}let score = 85;
if (score >= 90) {
console.log("Grade: A");
} else if (score >= 80) {
console.log("Grade: B");
} else {
console.log("Grade: C or lower");
}A shorthand way to write an if...else statement.
let isMember = true;
let discount = isMember ? "10% off" : "No discount";
console.log(discount);
let isMember = true;
let discount = isMember ? "10% off" : "No discount";
console.log(discount);
let isMember = true;
let discount = isMember ? "10% off" : "No discount";
console.log(discount);
The switch statement is used when checking multiple possible values of a variable.
let day = "Monday";
switch (day) {
case "Monday":
console.log("Start of the week.");
break;
case "Friday":
console.log("Weekend is near.");
break;
case "Sunday":
console.log("Relax, it's the weekend.");
break;
default:
console.log("A regular day.");
}let day = "Monday";
switch (day) {
case "Monday":
console.log("Start of the week.");
break;
case "Friday":
console.log("Weekend is near.");
break;
case "Sunday":
console.log("Relax, it's the weekend.");
break;
default:
console.log("A regular day.");
}let day = "Monday";
switch (day) {
case "Monday":
console.log("Start of the week.");
break;
case "Friday":
console.log("Weekend is near.");
break;
case "Sunday":
console.log("Relax, it's the weekend.");
break;
default:
console.log("A regular day.");
}break prevents fall-through execution to the next case.
default runs if no case matches.
Loops allow repetitive execution of code until a condition is met.
Used when the number of iterations is known.
for (let i = 1; i <= 5; i++) {
console.log("Iteration:", i);
}for (let i = 1; i <= 5; i++) {
console.log("Iteration:", i);
}for (let i = 1; i <= 5; i++) {
console.log("Iteration:", i);
}Executes as long as the condition remains true.
let count = 1;
while (count <= 5) {
console.log("Count:", count);
count++;
}let count = 1;
while (count <= 5) {
console.log("Count:", count);
count++;
}let count = 1;
while (count <= 5) {
console.log("Count:", count);
count++;
}Similar to while, but always executes at least once.
let num = 1;
do {
console.log("Number:", num);
num++;
} while (num <= 3);let num = 1;
do {
console.log("Number:", num);
num++;
} while (num <= 3);let num = 1;
do {
console.log("Number:", num);
num++;
} while (num <= 3);Exits a loop immediately.
for (let i = 1; i <= 10; i++) {
if (i === 5) {
break;
}
console.log(i);
}for (let i = 1; i <= 10; i++) {
if (i === 5) {
break;
}
console.log(i);
}for (let i = 1; i <= 10; i++) {
if (i === 5) {
break;
}
console.log(i);
}Output: 1 2 3 4 (stops at 5).
Skips the current iteration and continues with the next.
for (let i = 1; i <= 5; i++) {
if (i === 3) {
continue;
}
console.log(i);
}for (let i = 1; i <= 5; i++) {
if (i === 3) {
continue;
}
console.log(i);
}for (let i = 1; i <= 5; i++) {
if (i === 3) {
continue;
}
console.log(i);
}Output: 1 2 4 5 (skips 3).
This section covered conditional statements and loops, which control program flow. The next section will focus on functions, an essential part of writing reusable and structured JavaScript code.