How to get type information of a property type imported from another file in TypeScript Compiler API?

Question

How to get type information of property declaration whose type is a class from another file?

// person.ts

/**
 * @description Some description
 */
export class Person {
  name: string;
  constructor() { }
}

// group.ts

export class Group {
  member1: Person; // <-- Use TS typechecker to get info of Person class
  member2: Person;
  element: HTMLButtonElement; // <-- Getting all member and nodes for HtmlButtonElement using typechecker
  constructor() { }
}

Using TypeScript Compiler API

import ts from 'typescript';
const parsedCMD = ts.getParsedCommandLineOfConfigFile(
  `tsconfig.lib.json`,
  undefined,
  ts.sys as any
);
const files = parsedCMD.fileNames;
const program = ts.createProgram(files, parsedCMD.options);
const checker = program.getTypeChecker();
const sourceFile = program.getSourceFile('group.ts');

ts.forEachChild(sourceFile, (node: ts.Node) => {
  if (ts.isClassDeclaration(node)) {
    node.members.forEach(member => {
      if (ts.isPropertyDeclaration(member)) {
        const type = checker.getTypeAtLocation(member.name);
        console.log(type);
        /**
         * Output for element: HtmlButtonElement
         *
         * callSignatures: undefined
         * checker: {getNodeCount: ƒ, getIdentifierCount: ƒ, getSymbolCount: ƒ, getTypeCount: ƒ, 
         * getRelationCacheSizes: ƒ, …}
         * constructSignatures: undefined
         * flags: 524288
         * id: 74
         * members: undefined
         * numberIndexInfo: undefined
         * objectFlags: 2
         * properties: undefined
         * stringIndexInfo: undefined
         * symbol: SymbolObject {flags: 65, escapedName: "HTMLButtonElement", declarations: Array(2), * members: Map(20), parent: undefined, …}
         * Was able resolve Symbols and Nodes for HtmlButtonElement
         *
         */

        /**
         * Output for member1: Person
         * checker: {getNodeCount: ƒ, getIdentifierCount: ƒ, getSymbolCount: ƒ, getTypeCount: ƒ, 
         * getRelationCacheSizes: ƒ, …}
         * flags: 1
         * id: 4
         * intrinsicName: "error"
         * objectFlags: 0
         *
         * Getting error when using checker.getTypeAtLocation
         */
      }
    });
  }
});

I want to access members and jsDocComments for Person class at member1 location. I'm able to get all members or properties for HtmlButtonElement using checker.getTypeAtLocation but not for member1: Person. What am i missing?

Answer 1

You should check the diagnostics on the program (ts.getPreEmitDiagnostics(program)). You will find the following along with other errors:

error TS2304: Cannot find name 'Person'.

member1: Person;
         ~~~~~~

So after importing Person into that file...

import { Person } from "./person";

...you can do the following:

ts.forEachChild(groupFile, node => {
  if (ts.isClassDeclaration(node)) {
    for (const member of node.members) {
      if (ts.isPropertyDeclaration(member) && member.name.getText(groupFile) === "member1") {
        const personType = typeChecker.getTypeAtLocation(member.name);
        console.log(typeChecker.typeToString(personType));
        for (const property of personType.getProperties()) {
          console.log(property.name);
        }
      }
    }
  }
});

Outputs:

Person
name