Basic Types

You can create simple to advanced types with TypeScript. We’ve seen the string type, but let’s learn about more basic types.

number

let num1: number = 20
/**/num1/**/ = true

boolean

let isRaining: boolean = true
/**/isRaining/**/ = "false"

arrays

We can declare an array of strings like this:

let fruits: string[] = ["mango", "orange", "strawberry"]
fruits.push(/**/20/**/)

And an array of numbers like this:

let numbers: number[] = [20, 40, 60]
numbers.push(/**/"hello"/**/)

There’s also the Array type we can use like this:

let fruits: Array<string> = ["mango", "orange", "strawberry"]
fruits.push(/**/20/**/)

Here we are using the Array generic type. Don’t worry about this now. We’ll learn about generic types later.

tuples

Tuples are like arrays but with a fixed number of elements which are also typed. Here’s an example tuple:

let tuple: [string, number] = ["hello", 50]
tuple[/**/2/**/]

As you see above, trying to access an index not in the fixed length throws an error.

let tuple: [string, number] = ["hello", 50]
/**/tuple[0]/**/ = 20

From the above example, we assigned the 0 index to string so putting a number there throws an error.

undefined

let user: undefined = undefined
/**/user/**/ = {
  name: "deeecode"
}

object

You can also create an object type:

let user: {
  name: string;
  age: number;
  isLoggedIn: boolean
} = {
  name: "deeecode",
  age: 40,
  isLoggedIn: true
}

user./**/something/**/ = "hello"

Our type does not include a something field, so trying to add that field throws an error.

Looking at our object type, it’s possible that we want one of the fields to be optional. Maybe we don’t want the age field to be required. For that, we can use a question mark before the colon ?::

let user: {
  name: string;
  age?: number;
  isLoggedIn: boolean
} = {
  name: "deeecode",
  isLoggedIn: true
}

Since age is optional, we do not need to pass it.

We’ll learn about more ways we can type variables in the coming lessons.