henry-oliver-edwards / learning-project-2

Typescript Learning Course From Udemy Part 1

This is my learning repository from a course I took on Udemy for types

How to run this project

Needed: A version of node

• v19.9.0 used in this project

A package manager

• npm (usually comes with node)
• yarn (I used yarn for this project)
• pnpm (Relatively new, uses system links to save space)

A TypeScript compiler

• tsc npm install -g typescript
• yarn add global typescript
• pnpm add -g typescript

This set of documents goes over all the basics of typescript

Including:

1. Basic types ('number', 'string', 'boolean', etc) : in app.ts

2. Arrays and types of arrays, arrays can have a type as well, of you only wanted an array of strings, you could type string[] : in basics.ts

3. Objects are also types in Typescript if you make a regular object, TypeScript will automatically infer the type of the object, but you can also explicitly type it with an object before the object value; this is done with a colon and curly braces : {name: string, age: number} : in basics.ts

4. ENUMS are another TypeScript only feature, this is where you have a constant, and you want to don't want to keep making variables for these constants, enums prevent having to do this a just manage one structure and reference that structure : in enums.ts

5. Functions and return types, most functions will return some sort of value, this can be referenced with a type after the function parameters, function add(n1: number, n2: number): number { return n1 + n2; }. However, some functions will not return anything; these are called void functions, and instead of a type being at the end of a function, the void keyword is used.We can also alias functions in TypeScript where we assign a new variable to an existing function.This should be taken with caution though because our new function has to inherit the old type return of the old function.This can be a complicated concept, so an example is given below, they basically act as function definitions or prototypes, example here : in functions.ts

6. Unions are a way to have a variable be more than one type, this is done with the pipe operator |, it allows you to also use custom types or strings in these unions, this can simplify checking for types in functions and making logic easier and code more concise : in unions.ts

7. The last 2 types in TypeScript are unknown and never types, the unknown type is very similar to the any type, unknown types can be reassigned to any values. This type is useful when you don't know what you want your variable to be, but you want to make sure it is a certain type before you use it. The never type is used when you know a function will never return anything, this is useful for functions that throw errors or functions that have an infinite loop. : in unknown-never-type.ts

Function Aliasing Example

  function add(n1: number, n2: number): number {
    return n1 + n2
}

// This is an alias of a function that we have assigned to a variable
let myAdd: Function = add

let myAdd2: (a: number, b: number) => number;

//This line of TypeScript code defines a variable called myAdd2 with a specific function type. 
// The function type indicates that myAdd2 should be assigned a function that takes two parameters, both of type number, and returns a value of type number.

let myAdd2: (a: number, b: number) => number;

myAdd2 = function(a: number, b: number): number {
    return a + b;
};

console.log(myAdd2(10, 20)); // Output: 30