Just enough Typescript for Angular

Angular Framework is written in TypeScript. All of the pre-generated scripts and code samples are also in TypeScript. So, it makes total sense to get little bit familiar with TypeScript before we dive in to the world of Angular.

1. What is TypeScript?

  • TypeScript is a superset of Javascript, which means it is built on top of Javascript and fully supports Javascript syntax. It mainly provides optional static typing, classes and interfaces.

Why use TypeScript? The biggest advantage of using TypeScript instead of Javascript is that, it provides the IDEs to detect the errors in your code in compile time or as you type, not in runtime.

2. Variable declarations

There are two ways to declare variables in TS: Using var and let:

var - is scoped to the nearest function block. The scope is global when declared outside of the function. let - is scoped to the nearest enclosing statement or expression, which can be smaller than a function block.

Constants are declared using the keyword const. const - is scoped similar to var and allows you to create read only reference to a value. Constants declared with const must be initialized right away.

It is recommended to use only let and const to make your code more predictable and bug free.

3. Basic types

Below is the list of basic types in TS.

  1. Boolean
  2. Number
  3. String
  4. Array
  5. Tuple
  6. Any


let done: boolean = true
let done: boolean = false

Number In TypeScript, all numbers are floating point values, just like in Javascript.

const year: length = 10
const height: number = 6.1

String Strings can be declared using single quotes as well as double quotes.

const firstName = 'Michael'
const lastName = 'Jackson'

We can also use Template Strings with back-ticks which allow us to write multiline strings and embed expressions

let bintree = 'bintree.net'
let multiLineString = `
	Hi there,
	This is Sardor from ${bintree}


const myArray: number[] = [1, 2, 3] // Regular array type
let yourArray: Array<number> = [4, 5, 6] // Generic array type

Tuple When we want to declare an array with different variable types, we cannot use the regular array, we have to use Tuple.

let todo: [number, string, boolean] // Initialize
todo = [1, 'Go shopping', true] // Correct
todo = ['Go shopping', 1, true] // Incorrect. Order must be followed
todo[2] = true // Correct
todo[3] = 'Important' // Correct, because it is one of number|string|boolen

Any When we are not sure about the type of the variable we are creating or if it is going to be dynamically assigned, we can use the keyword any. It allows you to declare a variable that can be of any type.

let someVariable: any
someVariable = 2.2
someVariable = 'Now we re-assign a string'
someVariable = true
// Also, we can use it with arrays and assign mixed types of variables
let mixedArray: any[] = ['dog', 2, true]

For the complete list of types please refer to the TypeScript Documentation