简易版 co 实现

• 支持 promise 和 thunk 函数
• it.throw 会自动执行下 1 个 next

参考地址

co 里的 yield fn, fn 必须 function, promise, generator, array, object

function f1() {
  return new Promise((resolve, reject) => {
    setTimeout(() => {
      reject("f1");
    }, 1000);
  });
}
function f2() {
  return new Promise((resolve, reject) => {
    setTimeout(() => {
      resolve("f2");
    }, 1000);
  });
}

// thunk 函数
function f3(callback) {
  setTimeout(() => {
    callback(null, "thunk f3"); // thunk 函数
  }, 1000);
}

function f4() {
  return "f4";
}

function* main() {
  try {
    console.log(yield f1());
  } catch (e) {
    console.log("error", e);
  }
  console.log(yield f2());
  try {
    console.log(yield f3);
  } catch (e) {
    console.log("error", e);
  }
  console.log(yield f4());
  yield console.log("done");
}

function runGenerator(ge) {
  let it = ge();
  next(); // 启动

  function next(err, val) {
    let res;
    if (!err) {
      res = it.next(val);
    } else {
      res = it.throw(err);
    }
    if (!res.done) {
      nextWithVal(res.value, next);
    }
  }

  function nextWithVal(value, next) {
    if (value && value.then) {
      // Promise
      value.then((val) => next(null, val)).catch((err) => next(err));
    } else if (typeof value === "function") {
      // thunk 函数
      value((err, data) => {
        if (err) {
          next(err);
          return;
        }
        next(null, data);
      });
    } else {
      next(null, value);
    }
  }
}
runGenerator(main);

/*
    error f1
    f2
    thunk f3
    f4
    done
*/