How does TypeScript perform type checking?

TypeScript performs type checking at compile time, which means it analyzes the code before it's executed to ensure that the types of variables, function parameters, and return values are used correctly according to their declarations. This helps catch errors early in the development process and provides better tooling support like autocompletion and refactoring.

For example, consider the following TypeScript code:

function greet(name: string): string {
    return "Hello, " + name;
}

const userName: number = 25;
console.log(greet(userName));

In this example, the greet function expects a parameter of type string. However, userName is declared as a number. TypeScript's type checker will raise an error at compile time, indicating a type mismatch.

TypeScript uses a combination of static analysis and type annotations to perform this checking. Developers can explicitly declare types for variables, function parameters, and return values, or they can let TypeScript infer types based on the context in which they are used.

For cloud-based development, TypeScript's type checking can be integrated with various services. For instance, Tencent Cloud's Cloud Studio provides an integrated development environment (IDE) that supports TypeScript, allowing developers to leverage type checking and other features directly within their cloud-based workflow.