To get syntax highlighting in your editor (e.g. VS Code) you'll need to download typing information for the modules that you use in your project.
Say for example you use React and ReactDOM in your project, and you want to get highlighting and Intellisense for them. You will need to add the types to your project using this command:
npm install --save @types/react @types/react-dom
Your editor should now automatically pick up on on this typing information and supply you with autocomplete and Intellisense for these modules.