在异步等待中处理 try-catch 中的“抛出错误”是否有任何问题？

Question

我有一种使用 mongoose 将产品发布到 mongodb 的方法。我正在使用异步等待而不是 then-catch 块。我的代码：

const Category = require('../models/category');

exports.postProduct = async (req,res,next)=>{
    //const userId = req.user.userId;
    const userId = '5dca886a1ee97b07002de048';
    // const category = req.body.category;
    const category = ['bikes','cars'];
    // const tags = req.body.tags;
    const tags = ['wheels','vehicles','travel','s','s','s'];
    //const imageUrl = req.body.imageUrl;
    const imageUrl = ['https://picsum.photos/200/300','https://picsum.photos/200/300','https://picsum.photos/200/300'];
    try {
    if(tags.length>5){
        const error = new Error('Select only 5 Tags');
        error.statusCode = 406;
        throw error;
    }
    if (!category || category === []){
        const error = new Error('Selected category is empty, select category again');
        error.statusCode = 406;
        throw error;
    }
        const categoryFound = await Category.find({name: {$in:category}}).select('name');
        if (categoryFound) {
            const addProduct = new Product(
                {   name : 'vehicle',
                    description:'Its a good vehicle',
                    categoryId: categoryFound,
                    productImageUrl: imageUrl,
                    creatorId:userId,
                    productRequirement:'buy',
                    tags:tags
                });
          const productSaved = await addProduct.save();
        res.status(200).json({message:productSaved});
        }else{
            const error = new Error('Category not found!');
            error.statusCode = 404;
            throw error;
        }
    } catch (err) {
        if (!err.statusCode) {
            err.statusCode = 500;
        }
        next(err);
    }
};

catch 中的错误被我的 app.js 中的 express 中间件捕获。

//Error handling middleware
app.use((error, req, res, next) => {
    const status = error.statusCode || 500;
    const message = error.message;
    res.status(status).json({ message: message, status: status });
});

这很好用。在这种特定情况下，当数组“标签”长于 5 时，我从 Postman（REST API 开发工具）的请求返回：

{
    "message": "Select only 5 Tags",
    "status": 406
}

当我尝试在 try-catch 之外使用“if”检查时，我收到此错误：

 UnhandledPromiseRejectionWarning: Error: Select only 5 Tags
    at exports.postProduct (F:\project\controllers\products.js:17:23)
    at Layer.handle [as handle_request] (F:\project\node_modules\express\lib\router\layer.js:95:5)
    at next (F:\project\node_modules\express\lib\router\route.js:137:13)
    at Route.dispatch (F:\project\node_modules\express\lib\router\route.js:112:3)
    at Layer.handle [as handle_request] (F:\project\node_modules\express\lib\router\layer.js:95:5)
    at F:\project\node_modules\express\lib\router\index.js:281:22
    at Function.process_params (F:\project\node_modules\express\lib\router\index.js:335:12)
    at next (F:\project\node_modules\express\lib\router\index.js:275:10)
    at Function.handle (F:\project\node_modules\express\lib\router\index.js:174:3)
    at router (F:\project\node_modules\express\lib\router\index.js:47:12)
    at Layer.handle [as handle_request] (F:\project\node_modules\express\lib\router\layer.js:95:5)
    at trim_prefix (F:\project\node_modules\express\lib\router\index.js:317:13)
    at F:\project\node_modules\express\lib\router\index.js:284:7
    at Function.process_params (F:\project\node_modules\express\lib\router\index.js:335:12)
    at next (F:\project\node_modules\express\lib\router\index.js:275:10)
    at F:\project\app.js:54:5

这种在try-catch中抛出错误以检查长度，使用if语句检查空数组的方式是否有效？有没有更好的办法？

Answer 1

您正在抛出一个错误，但没有人能捕捉到它。当您创建 async 函数时，它会返回一个承诺。因此，当您抛出错误但未捕获它时，该函数将返回一个被拒绝的承诺。这就是您收到UnhandledPromiseRejectionWarning 的原因。当您使用 async/await 时，您必须使用 try-catch 捕获 Promise 拒绝。