requireTypeHintedFile.js

example.js

function test(asd: number, b: number) -> number {
  return asd + b;
}

function test2(x: string, y: string) -> boolean {
  return true;
}

module.exports = { test, test2 };

requireTypeHintedFile.js

const fs = require('fs');
const Module = require('module');
const path = require('path');
const util = require('util');
const debuglog = util.debuglog('module');

const FN_REGEX = /function (.+?) ?\((.+?)\) ?-> ?(.+?) ?{((.|\n)+?})/g;
const ARG_REGEX = /([^, (]+?): ?([^) ,]+)/g;

function typingRequire(filename) {
  let src = fs.readFileSync(filename).toString();
  for (const fnMatch of src.match(FN_REGEX)) {
    const ANNOTATION = {};
    const ARGUMENTS = [];
    FN_REGEX.tempIndex = FN_REGEX.lastIndex;
    FN_REGEX.lastIndex = 0;
    let [, name, args, returnType, body] = FN_REGEX.exec(fnMatch);
    body = body.replace(/}$/, '');
    FN_REGEX.lastIndex = FN_REGEX.tempIndex;
    for (const argMatch of args.match(ARG_REGEX)) {
      ARG_REGEX.tempIndex = ARG_REGEX.lastIndex;
      ARG_REGEX.lastIndex = 0;
      let [, argName, type] = ARG_REGEX.exec(argMatch);
      ANNOTATION[argName] = type;
      ARGUMENTS.push(argName);
      ARG_REGEX.lastIndex = ARG_REGEX.tempIndex;
    }
    ANNOTATION.return = returnType;
    src = src.replace(fnMatch,
`function ${name}(${Object.keys(ANNOTATION).filter(a => a !== 'return').join(',')}){${body}}
Object.defineProperties(${name},{
  annotation:{value:${JSON.stringify(ANNOTATION)}},
  args:{value:${JSON.stringify(ARGUMENTS)}},
})`);
  }
  const m = new Module(filename, module.parent);
  debuglog('load %j for module %j (TYPE REWRITE)', filename, m.id);
  m.filename = filename;
  m.paths = Module._nodeModulePaths(path.dirname(filename));
  m._compile(src, filename);
  return m.exports;
}

module.exports = typingRequire;