TypeScript overview

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:

1function myFunction(
2    isYearRound: boolean, 
3    cost: number,
4    destination: { name: string }
5) {
6    ...
7}
8

Breaking that down:

• the isYearRound variable has a primitive type of boolean
  • thus, isYearRound 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:

1function myFunction(
2    propertyX: type,
3    ...
4) {
5    ...
6}

• 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