mirror-types-for-deps.md

Item 70: Mirror Types to Sever Dependencies

Things to Remember

• Avoid transitive type dependencies in published npm modules.
• Use structural typing to sever dependencies that are nonessential.
• Don't force JavaScript users to depend on @types. Don't force web developers to depend on Node.js.

Code Samples

// parse-csv.ts
import {Buffer} from 'node:buffer';

function parseCSV(contents: string | Buffer): {[column: string]: string}[]  {
  if (typeof contents === 'object') {
    // It's a buffer
    return parseCSV(contents.toString('utf8'));
  }
  // ...
}

💻 playground

---

// parse-csv.d.ts
import { Buffer } from 'node:buffer';
export declare function parseCSV(contents: string | Buffer): {
    [column: string]: string;
}[];

💻 playground

---

export interface CsvBuffer {
  toString(encoding?: string): string;
}
export function parseCSV(
  contents: string | CsvBuffer
): {[column: string]: string}[]  {
  // ...
}

💻 playground

---

parseCSV(new Buffer("column1,column2\nval1,val2", "utf-8"));  // OK

💻 playground

---

/** Anything convertible to a string with an encoding, e.g. a Node buffer. */
export interface StringEncodable {
  toString(encoding?: string): string;
}

💻 playground

---

import {Buffer} from 'node:buffer';
import {parseCSV} from './parse-csv';

test('parse CSV in a buffer', () => {
  expect(
    parseCSV(new Buffer("column1,column2\nval1,val2", "utf-8"))
  ).toEqual(
    [{column1: 'val1', column2: 'val2'}]
  );
});

💻 playground