Explore all user-defined properties of a specified type using the TypeScript Compiler API

Consider the following model structure:

interface Address{
   country: string;
}

interface Author{
  authorId: number;
  authorName:string;
  address: Address;
}

interface Book{
  bookId:string;
  title: string;
  author : Author;
}

I want to iterate through all the properties of the Book interface.

const bookType = // obtain the type node of Book
const stack: any[] = [...bookType.getProperties()];
const props: any[] = [];

while (stack.length) {
  const prop = stack.pop();
  props.push(prop);
  if (checker.getTypeOfSymbolAtLocation(prop, node)) { //node is a ts.MethodDeclaration which returns a value of type Book
    stack.push(...checker.getTypeOfSymbolAtLocation(prop, node).getProperties());
  }
}

The code above successfully accomplishes this task, however, it also retrieves properties of built-in types like string, number etc., (e.g. toLocaleString, valueOf, toPrecision). I aim to specifically extract properties of custom types/interfaces and disregard built-in types.

Answer №1

The code snippet above is functional, but it retrieves properties from built-in types such as strings and numbers (e.g. toLocaleString, valueOf, toPrecision). To focus solely on custom type/interfaces and disregard built-in types, a different approach is needed.

One way to accomplish this is by navigating from the type to the symbol, then verifying if the symbol corresponds to any declarations within your project. Here's an example:

// This code is not tested, but serves as a guide
const type = checker.getTypeOfSymbolAtLocation(prop, node);
const isInYourProject = type.getSymbol()?.getDeclarations()?.some(d => {
  // Alternatively, you can check if the file path is not
  // in the `node_modules/typescript/lib` directory.
  return isFilePathInYourProject(d.getSourceFile().fileName);
});

if (isInYourProject) {
  // perform desired actions...
}

You can also utilize type.flags to determine whether the type is similar to string or number.

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