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If...Else in JavaScript

In JavaScript, the if...else statement is used to execute a block of code if a specified condition is true. If the condition is false, another block of code can be executed.

Syntax​

The syntax of the if...else statement is as follows:

app.js
if (condition) {
  // code to be executed if the condition is true
} else {
  // code to be executed if the condition is false
}

Example​

The following example demonstrates how to use the if...else statement to check if a number is even or odd:

app.js
let num = 10;

if (num % 2 === 0) {
  console.log(`${num} is even`);
} else {
  console.log(`${num} is odd`);
}

In the above example, the if...else statement checks if the number num is even or odd and logs the result to the console.

Nested if...else​

You can also use the if...else statement inside another if...else statement. This is known as a nested if...else statement.

The following example demonstrates how to use a nested if...else statement to check if a number is positive, negative, or zero:

app.js
let num = 10;

if (num > 0) {
  console.log(`${num} is positive`);
} else if (num < 0) {
  console.log(`${num} is negative`);
} else {
  console.log(`${num} is zero`);
}

In the above example, the nested if...else statement checks if the number num is positive, negative, or zero and logs the result to the console.

Ternary Operator​

The if...else statement can also be written using the ternary operator (? :).

The following example demonstrates how to use the ternary operator to check if a number is even or odd:

app.js
let num = 10;

const result = num % 2 === 0 ? `${num} is even` : `${num} is odd`;

console.log(result);

In the above example, the ternary operator checks if the number num is even or odd and assigns the result to the result variable.

📝 Note

Conditional Statements

The if...else statement is a conditional statement that executes a block of code if a specified condition is true. If the condition is false, another block of code can be executed.

In JavaScript we have the following conditional statements:

  • if statement: executes a block of code if a specified condition is true.
  • if...else statement: executes a block of code if a specified condition is true and another block of code if the condition is false.
  • if...else if...else statement: executes a block of code if a specified condition is true, another block of code if another condition is true, and another block of code if the conditions are false.
  • switch statement: selects one of many code blocks to be executed.
  • ternary operator: assigns a value to a variable based on a specified condition.
  • nullish coalescing operator: returns the right-hand operand when the left-hand operand is null or undefined.

Conclusion​

In this tutorial, we learned about the if...else statement in JavaScript. We learned how to use the if...else statement to make decisions in JavaScript. We also saw examples of how to use the if...else statement to check if a number is even or odd and to check if a number is positive, negative, or zero.