JavaScript Instance Examples

let regexp = new RegExp('ab+c');

let array = [1, 2, 3];

let set = new Set([1, 2, 3]);

TypeScript Annotations

let regexp: RegExp = new RegExp('ab+c');

let array: Array<number> = [1, 2, 3];

let set: Set<number> = new Set([1, 2, 3]);

Sneak Peek At Custom Classes

/** A first in first out collection */
class Queue<T> {
  private data: Array<T> = [];
  push(item: T) { this.data.push(item); }
  pop(): T | undefined { return this.data.shift(); }
}

Instance type annotation:

let queue: Queue<number> = new Queue();

Transcript

00:01

Now JavaScript, despite being a functional programming language at its core, does support classes. And there are a number of built-in classes for JavaScript run times out there. One of them is the class for regular expressions. Another built-in class that is used quite heavily within JavaScript code is the class for an array Now, because arrays are something that you will use quite heavily, JavaScript provides special syntax to create JavaScript arrays. Now, modern JavaScript runtimes also come

00:33

with additional collection classes, and one of them is a set class, which is used for a unique set of items. We can initialize the set with a JavaScript array, and internally it'll remove any duplicates that are found within that array. Now we can annotate instances of these classes simply by using the class name. Now for classes like Array that support generics, and don't worry, generics are something that we will look at in another lesson. You will also have to pass in the generic argument. Since we have an array of numbers over here,

01:06

we will use the annotation array of type number. Similarly, we have a set of numbers over here, so the annotation for that will be a set of type number. Now, in addition to these and other built-in JavaScript classes, you can actually create a class in JavaScript yourself as well. Here we have a generic class for a queue, which is a first in first out collection. Now we will have a separate lesson on JavaScript classes as well, so the details of this class are not that important. Now, just like the built-in JavaScript classes like Array

01:41

and Set, we can use the user created class in a type annotation. Here we have a variable queue, which is annotated to be a queue of type number.

Professional TypeScript Masterclass Lessons

Instance Types

JavaScript Instance Examples

TypeScript Annotations

Sneak Peek At Custom Classes

Transcript

Professional TypeScript Masterclass