JavaScript Tutorial
Conditionals let your program choose different paths based on a condition.
They power decision making in forms, UI flows, validation, and business rules.
Every real app needs branching logic. Without conditionals, code cannot respond to user input or data.
Understanding conditionals keeps your logic predictable and easy to maintain.
if (condition) { ... }
if (condition) { ... } else { ... }
if (a) { ... } else if (b) { ... } else { ... }
switch (value) { case x: ...; break; default: ... }const loggedIn = true;
if (loggedIn) {
console.log("Welcome back");
}Run a block only when the condition is true.
const isMember = false;
if (isMember) {
console.log("Member price");
} else {
console.log("Standard price");
}Provide a fallback branch for the false case.
Conditionals control which code runs based on a boolean expression. They are the core of business rules and UI states.
Use if/else for flexible logic and switch when you have a single value with multiple discrete cases.
Readable conditions reduce bugs. Prefer small, named boolean variables over long, nested expressions.
Parentheses can improve clarity when mixing logical operators.
Switch statements are ideal for mapping a single value to many outcomes.
Remember to use `break` to avoid fall-through unless that is your intent.
JavaScript treats some values as falsy: 0, "", null, undefined, NaN, and false.
Be explicit when a value like 0 or an empty string is meaningful.
const score = 82;
let grade;
if (score >= 90) {
grade = "A";
} else if (score >= 80) {
grade = "B";
} else if (score >= 70) {
grade = "C";
} else {
...Use else-if ladders for ranges or tiers.
const role = "admin";
switch (role) {
case "admin":
console.log("All access");
break;
case "editor":
console.log("Write access");
break;
default:
...Switch maps a single value to multiple outcomes.
Without
let label;
if (status === "paid") {
label = "Paid";
} else {
label = "Pending";
}With
const label = status === "paid" ? "Paid" : "Pending";Add an else when you need a clear fallback path.
Split into named boolean variables for readability.
Add break to avoid accidental fall-through.
Use explicit comparisons when values like 0 or "" are valid.
If is flexible for many conditions; switch compares one value against cases.
When a case runs into the next because break is missing.
They reduce readability and are harder to debug.
Practice: Build a status label using if/else based on a payment status string.
const status = "processing";
// TODO: print a label for paid, failed, or pending
One Possible Solution
const status = "processing";
let label;
if (status === "paid") {
label = "Paid";
} else if (status === "failed") {
label = "Failed";
} else {
label = "Pending";
}
console.log(label);Use switch when you compare a single value against many discrete cases.
A chain of if/else-if blocks for multiple conditions.
No, only when you want a fallback action.
0, "", null, undefined, NaN, and false are falsy in JavaScript.
Try the conditional examples and change the inputs to see different branches.