TypeScript builds upon JavaScript by introducing optional static typing. This means developers can define the data types of variables and functions, enhancing code reliability and maintainability. Think of it as adding a layer of checks before running the code, catching potential errors early in the development process. TypeScript leverages familiar JavaScript syntax, making it a smooth transition for developers already comfortable with JavaScript. This characteristic, coupled with its ability to catch errors early, makes TypeScript a popular choice for building large-scale web applications.