Introduction to the JavaScript if statement

The if statement executes block if a condition is true. The following shows the syntax of the if statement

if( condition )
 statement;
Code language: JavaScript (javascript)

The condition can be a value or an expression. Typically, the condition evaluates to a Boolean value, which is true or false. If the condition evaluates to true, the if statement executes the statement. Otherwise, the if statement passes the control to the next statement after it.
The following flowchart illustrates how the if statement works

If the condition evaluates to a non-Boolean value, JavaScript implicitly converts its result to a Boolean value by calling the Boolean() function. If you have more than one statement to execute, you need to use wrap them in a block using a pair of curly braces as follows:

if (condition) {
 // statements to execute
}
Code language: JavaScript (javascript)

However, it’s a good practice to always use curly braces with the if statement. By doing this, you make your code easier to maintain and avoid possible mistakes.
JavaScript if statement examples
The following example uses the if statement to check if the age is equal to or greater than 18:

let age = 18;
if (age >= 18) {
 console.log('You can sign up');
}
Code language: JavaScript (javascript)

Output

You can sign up
Code language: JavaScript (javascript)

How it works.
First, declare and initialize the variable age to 18:

let age = 18;
Code language: JavaScript (javascript)

Second, check if the age is greater or equal to 18 using the if statement. Because the expression age >= 18 is true, the code inside the if statement executes that outputs a message to the console:

if (age >= 18) {
 console.log('You can sign up');
}
Code language: JavaScript (javascript)

The following example also uses the if statement. However, the age is 16 which causes the condition to evaluate to false. Therefore, you won’t see any message in the output:

let age = 16;
if (age >= 18) {
console.log('You can sign up');
}
Code language: JavaScript (javascript)

Nested if statement

It’s possible to use an if statement inside another if statement. For example:

let age = 16;
let state = 'CA';
if (state == 'CA') {
 if (age >= 16) {
 console.log('You can drive.');
 }
}

Output

You can drive.
Code language: JavaScript (javascript)

How it works.
First, declare and initialize the age and state variables:

let age = 16;
let state = 'CA';
Code language: JavaScript (javascript)

Second, check if the state is ‘CA’ using an if statement. If yes, check if the age is greater than 16 using a nested if statement and output a message to the console:

if (state == 'CA') {
 if (age == 16) {
 console.log('You can drive.');
 }
}

In practice, you should avoid using nested if statements as much as possible. For example, you can use the && operator to combine the conditions and use an if statements as follows:

let age = 16;
let state = 'CA';
if (state == 'CA' && age == 16) {
console.log('You can drive.');