🟦TypeScript

checking the validity of JavaScript types with a library

TypeScript extends JavaScript to ensure that a variable's data conforms to a certain form, or "type"!

Why TypeScript?

TypeScript allows for easier debugging and prevents bad data from circulating through an app:

• also, all JavaScript works in TypeScript

• however, TypeScript must transpile into JavaScript to work on the web

The essence of TypeScript

We use TypeScript to validate variables by assigning each variable in TypeScript a type:

function myFunction(
    yearRound: boolean, 
    cost: number,
    destination: { name: string }
) {
    ...
}

Breaking that down:

• the yearRound variable has a primitive type of boolean

  • thus, yearRound can only be either true or false

• the cost has a type of a number

  • (JavaScript has no integers or floats; all numeric data are just numbers)

  • thus, cost cannot have symbols other than digits and legal operators

• the destination has the type of an object {}

  • this object, in turn, contains a property called name

    • the name has a type of string

Abstracting that further:

function myFunction(
    propertyX: type,
    ...
) {
    ...
}

• type can take on any of the following (with a few more others):

  • string

  • number

  • boolean

  • Date

  • unknown

  • void

  • never

• the type can also be arrays of each of the above, e.g.

  • string[]

  • number[]

• as shown in the earlier top snippet, the type can also be an object

  • the properties in that object would also get their own types