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javascript - for-of 循​​环和异步函数的问题

问题描述

我想等到我的函数 checkNumber() 完成并返回结果。不幸的是，for-off 循环不会等待函数并在开始时进行所有迭代。我尝试了许多与 async/await 的组合，但没有一个真正起作用。当我运行这个函数时，它会打印出与循环一样多的 console.log("start error")，然后我得到 productList。当 checkNumber() 返回错误时，我想停止 for 循环。

主功能：

  if (!req.body) {
    res.status(400).send({
      message: "Values can not be empty!"
    });
  }

  console.log("list of products: ", req.body.product);
  const productArr = req.body.product; //array of products retrieved from json
  let productList = [];
  let quantityList = [];
  let error = 0;
  for (const product of productArr) { //iterate through products

    console.log("start error: ", error); // <---- 
    if (error == 1) {
      console.log("stop");
      break;
    }

    //check if product's vat exists in vat table, if not add new
    Vat.checkNumber(product.vat, async function (err, data) {
      console.log("result: ", data);
      if (!data) {
        console.log("not found");
        console.log(err);
        error = 1;
      } else {
        console.log("found");
        const vat_id = data;

        //crete new product obj json
        let newProduct = {
          vat_id: vat_id,
          name: product.name,
          price: product.price
        };

        //store product list and their quantity to use later in sql query
        productList.push(newProduct);
        quantityList.push(product.quantity);
        console.log(productList);
        console.log(quantityList);


      }
    });
  }
}

增值税功能：

  sql.query("SELECT * FROM vat where number = ?", number, function (err, res) {
    if (err) {
      console.log("error: ", err);
      result(err, null);
      return;
    }

    if (res.length <= 0) {
      err = "Vat cannot be null";
      result({ error: "Vat not found" }, null);
      return;
    }

    console.log("Found vat: ", res[0].id);
    result(null, res[0].id);
    return;
  });
};

标签： javascriptnode.jsexpressasynchronous

解决方案

试试这个：

async function checkNumber(number) {
  return new Promise((resolve, reject) => {
    sql.query('SELECT * FROM vat where number = ?', number, function(err, res) {
      if (err) {
        console.log('error: ', err);
        reject(err);
        return;
      }

      if (res.length <= 0) {
        err = 'Vat cannot be null';
        reject({ error: 'Vat not found' });
        return;
      }

      console.log('Found vat: ', res[0].id);
      resolve(res[0].id);
    });
  });
}

进而

for (const product of productArr) { //iterate through products

  console.log("start error: ", error); // <---- 
  if (error == 1) {
    console.log("stop");
    break;
  }

  //check if product's vat exists in vat table, if not add new
  let data; 
  try {
    data = await checkNumberPromisified(product.vat);
    if (!data) {
      console.log("not found");
      error = 1;
    } else {
      console.log("found");
      const vat_id = data;

      //crete new product obj json
      let newProduct = {
        vat_id: vat_id,
        name: product.name,
        price: product.price
      };

      //store product list and their quantity to use later in sql query
      productList.push(newProduct);
      quantityList.push(product.quantity);
      console.log(productList);
      console.log(quantityList);
    }
  }
  catch (err) {
    console.log(err);
    error = 1;
  }
}

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