7.2 - Typescript

Why typescript

Why typescript

1. Typescript is a superset of JS

2. It gives you static typing

3. Makes your code more strict 😢

What is static typing?

Lets convert a small JS file to TS

JS

TS

How to add types

What about functions?

(Try it yourself - 5 minutes)

Lets write a calculator

(5 minutes)

1. Function has 3 arguments, first, second and type

2. type is a string which can be 

a. "add", "div", "mul", "sub"

Problem ?

It's not strict enough

Solution

Union operator

Solution

Union operator

TS vs JS

How does JS run code

TS vs JS

How does TS run code? It never does

It does
1. Type checking

2. converts to JS

What is the TS compiler?

The compiler is called - tsc

Let's bring the counter code locally

npm i -g tsc

The tsconfig file

 tsc --init

target

ECMAScript version

1. es3, es5

very old (if u want to support IE)

2. ES2016 - ES2020

incrementally better

3. esnext

Latest

module

module type - target system

1. none

This isn't a module

2. commonjs

Node.js code

3. amd

browser code

Lets try commonjs vs es6

forceConsistentCasingInFileNames

Does casing matter when importing modules

strict

How strictly should TS be evaluated

Constraints

Interfaces, types and enums

Interfaces

(Person interface)

1. Let you accumulate data of a specific type

2. Interfaces can use other interfaces

3. Interfaces can extend interfaces

4. Interfaces can be implemented by classes

Types

Very slightly different from interfaces

Need to be equated

Very useful for unions and ors

Can not be extended

Differences b/w types and interfaces

Can mostly be used interchangibly

1. Interfaces can be implemented by classes

2. Interfaces can extend each other

3. Types can do unions and intersections

Enums