The Basics
To install the typescript compiler globally npm install -g typescript
Emitting with Errors, even tsc reports errors it still emits js files to stop it run tsc --noEmitOnError hello.ts
Erased Types, after processing ts files with tsc, type annotations are erased, it can also downlevel the js code to ES3 version by default. we can set the target using this command tsc --target es2015 hello.ts
Strictness
noImplicitAny Turning on the noImplicitAny flag will issue an error on any variables whose type is implicitly inferred as any.
strictNullChecks By default, values like null and undefined are assignable to any other type