TIL: Typescript Basics

Typescript:

• is a superset of Javascript
• transpiles to javascript
• offers strict typing features
• which help catch typing errors sooner

Typescript Syntax

We can (must) set variable types:

let name: string = "Michael";
let IQ: number = 215;

or function argument and return types:

function processThing(thingId: string ): string{
    // do something
    return "output";
}

We have 7ish primitive types available:

1. string
2. number
3. boolean
4. bigint
5. undefined
6. null
7. symbol (ES6+)

We also have some other, more special types:

1. object
2. any see gradual typing

Object Typing

It can be as simple as this:

let myFoo: object = {};

or we can also specify the object with fields itself:

let myFoo: object = {
    name: string;
    rank: number;
    createDate: Date;
};

Type Inference

Typescript can "infer" types from method return values, for example:

function getItem(): string {
    return "hi!";
}
// type is automatically inferred to be a String
let myItem = getItem();

Gradual Typing

Allows you to choose how and when types are applied by using the any type:

// basically, fall back to dynamic javascript typing
let cost: any = 425;
// alternate syntax
let cost = 425 as any;

Using the any type is essentially "opting out" of typescript static typing features.

Interfaces

A minimal interface might look like this:

interface book {
    name: string;
    rank: number;
    publishDate: Date;
};