JavaScript if/else statements
last modified April 16, 2025
In this article we show how to control program flow using the if and
else keywords in JavaScript.
The if/else keywords
The if statement executes a block of code if a specified condition
is true. The else statement executes a block if the same condition
is false. These are fundamental building blocks for decision-making in programs.
JavaScript evaluates the condition inside parentheses after if. If
the result is truthy, the code block executes. If falsy and an else
exists, that block executes instead. Conditions can be any expression that
returns a boolean value.
The else if construct allows testing multiple conditions in sequence.
Only one block will execute - the first one whose condition evaluates to true.
This provides a way to handle multiple possible cases.
Basic if statement
The simplest form of conditional execution uses just the if keyword.
const age = 20;
if (age >= 18) {
console.log("You are an adult");
}
This code checks if the age variable is 18 or greater. If true, it logs a message to the console. The code block only executes when the condition evaluates to true. No action occurs if the condition is false.
$ node main.js You are an adult
if with else
Adding an else clause provides an alternative execution path.
const temperature = 25;
if (temperature > 30) {
console.log("It's hot outside");
} else {
console.log("It's not too hot");
}
Here, one of two messages will always be printed. If temperature exceeds 30, the first message appears. Otherwise, the second message appears. The else block executes when the if condition is false.
$ node main.js It's not too hot
Multiple conditions with else if
Chain conditions together using else if for more complex logic.
const 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: D or below");
}
This example demonstrates a grading system. Conditions are checked in order until one matches. Only the first matching block executes. The final else catches all remaining cases not covered by previous conditions.
$ node main.js Grade: B
Nested if statements
if statements can be nested inside other if statements for complex conditions.
const age = 25;
const hasLicense = true;
if (age >= 18) {
if (hasLicense) {
console.log("You can drive");
} else {
console.log("You need a license");
}
} else {
console.log("You're too young to drive");
}
The outer if checks age, while the inner if checks license status. This structure allows combining multiple conditions in a logical way. Each condition must be true for the innermost block to execute.
$ node main.js You can drive
Logical operators in conditions
Logical operators like AND (&&) and OR (||) can combine conditions.
const hour = 14;
const isWeekend = false;
if (hour >= 9 && hour <= 17 && !isWeekend) {
console.log("Office is open");
} else {
console.log("Office is closed");
}
This example checks if current hour is between 9-5 and it's not a weekend. The
&& operator requires all conditions to be true. The !
operator negates the boolean value. Complex conditions become more readable.
$ node main.js Office is open
Ternary operator alternative
Simple if/else statements can be written concisely with the ternary operator.
const isMember = true;
const discount = isMember ? 0.1 : 0;
console.log(`Your discount is ${discount * 100}%`);
The ternary operator ? : provides a shorthand for simple conditionals.
If isMember is true, discount is 0.1 (10%), otherwise 0. This is equivalent to
a full if/else statement but more compact for simple cases.
$ node main.js Your discount is 10%
Truthy and falsy values
JavaScript conditions evaluate any value, not just booleans, using truthy/falsy rules.
const name = "";
const items = [1, 2, 3];
if (name) {
console.log(`Hello ${name}`);
} else {
console.log("Please enter your name");
}
if (items.length) {
console.log(`You have ${items.length} items`);
}
Empty strings are falsy, while non-empty strings are truthy. Arrays with length > 0 are truthy. Other falsy values include 0, null, undefined, NaN, and false. All other values are truthy. This behavior is unique to JavaScript.
$ node main.js Please enter your name You have 3 items
Source
if...else - language reference
In this article we have demonstrated how to use if/else statements to control program flow in JavaScript.