most_basic_parser.js

function getFunctionParametersFromString(funcStr) {
  const match = funcStr.match(/(?:function.*?\(|\()(.*?)(?:\)|=>)/);
  if (match && match[1]) {
    return match[1].split(',').map(p => p.trim());
  }

  return [];
}

function getFunctionParameters(func) {
  return getFunctionParametersFromString(func.toString());
}

function analyzeParameter(param) {
  const decoratorMatch = param.match(/@(\w+)\(([^)]+)\)/);
  const defaultValueMatch = param.match(/(.*?)=(.*)/);
  const isRestOrSpread = param.startsWith('...');

  let decorators = [];
  if (decoratorMatch) {
    const [_, decoratorName, decoratorArgs] = decoratorMatch;
    decorators.push({
      name: decoratorName,
      args: decoratorArgs.split(',').map(arg => arg.trim())
    });
  }

  const paramName = (isRestOrSpread ? param.substr(3) : param).trim();

  if (defaultValueMatch) {
    const [_, name, defaultValue] = defaultValueMatch;
    return {
      parameter: paramName,
      defaultValue: defaultValue.trim(),
      isRestOrSpread: isRestOrSpread,
      decorators: decorators
    };
  } else {
    return {
      parameter: paramName,
      defaultValue: null,
      isRestOrSpread: isRestOrSpread,
      decorators: decorators
    };
  }
}

/*
const params = getFunctionParameters(function test(
  a,
  b = 5,
  ...c
) { console.log(a, b, c); })

console.log(params.map(analyzeParameter));

---

const exampleFunc = 'function(@defaultValue(["a"]) a, @defaultValue(5, false) b, ...rest) {};';
const params = getFunctionParametersFromString(exampleFunc).map(analyzeParameter)
*/