TypeScript if-else Statements

Introduction

In this chapter, we will explore if-else statements in TypeScript. These control flow statements allow you to execute different blocks of code based on certain conditions. Understanding how to use if-else statements is essential for writing logical and efficient TypeScript programs.

Table of Contents

• If Statement
• If-Else Statement
• Nested If-Else Statement
• Ternary Operator
• Complete Example with Output
• Conclusion

If Statement

The if statement executes a block of code if a specified condition is true.

Syntax

if (condition) { // code to be executed if the condition is true } 

Example

This example checks if the variable age is greater than or equal to 18 and prints a message accordingly.

let age: number = 18; if (age >= 18) { console.log("You are an adult."); } 

Output

You are an adult. 

If-Else Statement

The if-else statement executes one block of code if a specified condition is true and another block of code if the condition is false.

Syntax

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

Example

This example checks if the variable age is greater than or equal to 18 and prints a message accordingly. If the condition is false, it prints a different message.

let age: number = 16; if (age >= 18) { console.log("You are an adult."); } else { console.log("You are a minor."); } 

Output

You are a minor. 

Nested If-Else Statement

The nested if-else statement is an if statement inside another if or else block. It allows for multiple levels of condition checking.

Syntax

if (condition1) { // code to be executed if condition1 is true if (condition2) { // code to be executed if condition2 is true } else { // code to be executed if condition2 is false } } else { // code to be executed if condition1 is false } 

Example

This example checks if age is greater than or equal to 18 and further checks if age is greater than or equal to 21.

let age: number = 20; if (age >= 18) { console.log("You are an adult."); if (age >= 21) { console.log("You can drink alcohol."); } else { console.log("You cannot drink alcohol."); } } else { console.log("You are a minor."); } 

Output

You are an adult. You cannot drink alcohol. 

Ternary Operator

The ternary operator is a shorthand for the if-else statement. It evaluates a condition and returns one value if true and another value if false.

Syntax

condition ? expressionIfTrue : expressionIfFalse 

Example

This example checks if age is greater than or equal to 18 and assigns a message accordingly using the ternary operator.

let age: number = 18; let message: string = age >= 18 ? "You are an adult." : "You are a minor."; console.log(message); 

Output

You are an adult. 

Complete Example with Output

In this section, we will combine all the examples into a single TypeScript file, compile it to JavaScript, and run it to see the output.

TypeScript Code

You can test the following code in the TypeScript Playground:

// If Statement let age: number = 18; if (age >= 18) { console.log("You are an adult."); } // If-Else Statement age = 16; if (age >= 18) { console.log("You are an adult."); } else { console.log("You are a minor."); } // Nested If-Else Statement age = 20; if (age >= 18) { console.log("You are an adult."); if (age >= 21) { console.log("You can drink alcohol."); } else { console.log("You cannot drink alcohol."); } } else { console.log("You are a minor."); } // Ternary Operator age = 18; let message: string = age >= 18 ? "You are an adult." : "You are a minor."; console.log(message); 

Conclusion

In this chapter, we covered the if statement, if-else statement, nested if-else statement, and ternary operator in TypeScript. We provided a complete example with its output to illustrate how these statements work in TypeScript. Understanding if-else statements is essential for writing logical and efficient TypeScript programs.