TypeScript has its types and also allows us to write our own custom types.

Core Types

These work on JS and TS.

1. number - numbers, decimals, negative numbers all come under this type.

2. string - text.

3. boolean - true, false.

   

   

   Note in the add() arguments we are saying explicitly that the arguments will be number.

   

   TypeScript is statically typed, which means we define the types of variables and parameters hands on during development.

   Key difference between TS and JS:

   

   and it is better to fail during development then during runtime.

Type Casting

Type Assignment & Type Inference

Here you can see below when i am doing const number1 = 5, const number2 = 2.8, etc. I am not assigning any type like I did in the function arguments. This is because of a TS feature called inference. Which means TS does its best to identify the type of the variable. So, it will know that number1 is a number and so on. Now, we can add : number in this as well, but it is not considered to be a good practice since the TS does a pretty good job infering it. Now, there is one condition in which you should do this. Which is when you are not initializing, you do it like this:

Object types

Contain key value pairs. Now consider: