Why Do We Need to Use Typescript?

This was what I thought when I started using Typescript.

I knew Typescript a couple of years ago. At that time, I thought it would sound good. However, I didn't need to use it since at that time I didn't use React.js and project I worked wasn't really using js.

Then, I met my friend who loves Typescript during I was working for my startup.

He always told me Use Typescript because it's legit!!!!

I was like "Okay man, I will try it soon." I didn't think about it seriously. Actually, I tried a couple of tutorials (very simple and small). Unfortunately, I didn't see its necessity.

Later 1 year, I started working on React.js + Typescript.
My co-workers told me about the necessity of Typescript. In theory, I could understand that, but to be honest it didn't hit me since I had a kind of tough time with Typescript.

However, now it really hit me.

I agree with this and what my friend told.
https://dzone.com/articles/what-is-typescript-and-why-use-it

The thing that really hit me is readability.
When I read Nodejs project code a couple of weeks ago, I got really confused since I wasn't familiar with the variable naming rule of the project, so really tough to predict the type of variables.

But, I don't think everyone should use Typescript
I guess to start using Typescript there should be a couple of things

Members are familiar with ES6
A transition period is predictable
There is a person familiar with webpack

Simple template reactjs+typescript
https://github.com/koji/webdev

The thing is that I haven't finished my portfolio site with react+typescript lol