what is typescript

Basically, TypeScript is like an extension or "superset" of JavaScript.
Since JavaScript is a loosely typed language,
TypeScript enforces the strict use of types. 
Thus, making it a strictly typed language.

TypeScript is an open-source programming language developed and maintained by Microsoft. It is a strict syntactical superset of JavaScript, and adds optional static typing to the language. 

TypeScript is designed for development of large applications and transcompiles to JavaScript.

Starts and ends with JavaScript
TypeScript starts from the same syntax and semantics that millions of JavaScript developers know today. Use existing JavaScript code, incorporate popular JavaScript libraries, and call TypeScript code from JavaScript.

TypeScript compiles to clean, simple JavaScript code which runs on any browser, in Node.js, or in any JavaScript engine that supports ECMAScript 3 (or newer).

TypeScript is an open-source programming language developed and maintained
by Microsoft.

It is a strict syntactical superset of JavaScript, and adds optional static
typing to the language. 

TypeScript is designed for development of large applications and transcompiles
to JavaScript.