javascript - 在异步等待中的try-catch中处理 'throw error'是否有问题？

Question

我有一种使用 Mongoose 将产品发布到mongodb中的方法。我正在使用async await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);
    }
};

捕获内的错误由我的app.js中的快速中间件捕获。

//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。在这种特定情况下，当数组“标签”长于5时，我来自Postman(REST API开发工具)的请求将返回:

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

当我尝试在try-catch之外使用'if'检查时，出现此错误:

 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法有效吗？有什么更好的方法吗？

Answer 1

那不是很明显吗？您正在抛出一个错误，但是没有人可以捕获它。创建async函数时，它会返回一个promise。因此，当您抛出错误但没有捕获错误时，该函数将返回被拒绝的promise。这就是为什么您得到UnhandledPromiseRejectionWarning的原因。当您使用异步/等待时，必须使用try-catch捕获 promise 拒绝。