Notice: This page requires JavaScript to function properly.
Please enable JavaScript in your browser settings or update your browser.
Learn If-else statement | Conditional Statements
Introduction to TypeScript

book
If-else statement

Sometimes, one condition is not enough, and for that, in TypeScript (as in other programming languages), there is the if-else construct. For example, if you need to create a calculator, you, as a true programmer, will do it using the if-else construct, like this:

let a: number = 5;
let b: number = 10;
let operator: string = '*';
if (operator == '+') {
console.log(a + b);
} else if (operator == '-') {
console.log(a - b);
} else if (operator == '*') {
console.log(a * b);
} else if (operator == '/') {
console.log(a / b);
} else {
console.log(`Error, there is no ${operator} operator!`)
}
1234567891011121314
let a: number = 5; let b: number = 10; let operator: string = '*'; if (operator == '+') { console.log(a + b); } else if (operator == '-') { console.log(a - b); } else if (operator == '*') { console.log(a * b); } else if (operator == '/') { console.log(a / b); } else { console.log(`Error, there is no ${operator} operator!`) }
copy

In this code, we have 3 variables: number a, number b, and the operation that will be performed between them. Using the if-else construct, we determine which operation will be applied to these two numbers. If we don't find a suitable operation, we will display a message indicating that such an operation is not available!

Now let's take a closer look at the syntax we're using:

javascript
if (first_condition) {
// code block if the first condition is true
} else if (second_condition) {
/* A block of code that will execute
if the first condition is false
and the second condition is true. */
} else if... {
// You can have as many of these blocks as you want.
} else {
/* A block of code that will execute
if all previous conditions are false. */
}

Note that if one of the conditions is met, we exit the if-else statement, and the remaining blocks are ignored.

Unlike else if, the else block does not have a condition block. This is because else executes only if all previous conditions were false.

The if-else construct is often used for a variety of tasks, from checking if a number is positive to writing artificial intelligence.

You can also choose not to use else-if blocks and use only if and else, for example:

let num: number = 15;
if (num >= 0) {
console.log('The number is positive!');
} else {
console.log('The number is negative');
}
123456
let num: number = 15; if (num >= 0) { console.log('The number is positive!'); } else { console.log('The number is negative'); }
copy

This way, we can experiment and use such a construct for various purposes!

1. What is the purpose of the if-else statement in TypeScript?

2. In an if-else statement, what is executed if the condition inside the if block is false?

question mark

What is the purpose of the if-else statement in TypeScript?

Select the correct answer

question mark

In an if-else statement, what is executed if the condition inside the if block is false?

Select the correct answer

Everything was clear?

How can we improve it?

Thanks for your feedback!

Section 2. Chapter 3

Ask AI

expand
ChatGPT

Ask anything or try one of the suggested questions to begin our chat

We use cookies to make your experience better!
some-alt