TypeScript also works wonders in React. Using a component that someone else made? TypeScript will make sure you are passing it the props it expects. Change the expected props for a component? TypeScript will immediately let you know what code you need to change for every component that uses that component.
Also NoImplicitAny and StrictNullChecks are two great tastes that taste great together. Everything in your code is now typed, AND TypeScript will now actually make you think about how you are handling (or not handling) null values. These two flags have basically allowed us to completely eliminate all the 'X is not a function of Y' and 'Z is undefined in this' errors - which is pretty amazing because for me at least these were probably the most common JS errors I get.
Also NoImplicitAny and StrictNullChecks are two great tastes that taste great together. Everything in your code is now typed, AND TypeScript will now actually make you think about how you are handling (or not handling) null values. These two flags have basically allowed us to completely eliminate all the 'X is not a function of Y' and 'Z is undefined in this' errors - which is pretty amazing because for me at least these were probably the most common JS errors I get.