异步/等待运行异步函数在nodejs中按顺序运行

Question

问题

我有三个相互依赖的函数，因此我希望它们能够连续运行。调用的函数是异步函数和返回承诺函数，运行起来需要时间。

我的代码- Index.js

#Function One
scrapA.scrap().then(data => {
    readWriteToFile.writeToFile(data, 'scrapA-data-'+timestamp, 'json');
});

#Function Two
compare.compareData('./output/json/data.json', './output/json/scraped-data-'+timestamp+'.json').then(data => {

    let dataWithStockData = data;
    let mapDatas = dataWithStockData.map( obj => { 

        let finalObj = {
            manufacturer: obj.manufacturer,
            grade: obj.condition,
            carrier: obj.carrier,
            stock: obj.stock,
        }
        return finalObj;
    });

#Function Three
readWriteToFile.writeToFile(data, 'data-with-stock-'+timestamp, 'csv'); });

我的代码- compare.js

async function compareData(models, competitorsData) {

try {
    
    const modelsArr = JSON.parse(fs.readFileSync(models, { encoding: 'utf8', flag: 'r' }));
    const competitorsDataArr = JSON.parse(fs.readFileSync(competitorsData, { encoding: 'utf8', flag: 'r' }));

    //Loop through both array of json data
    modelsArr.forEach((device, deviceKey) => {

        competitorsDataArr.forEach((scrapedData, scrapedDataKey) => {

            
            if (
                    scrapedData.manufacturer.toLowerCase() === data.manufacturer.toLowerCase()
            ) {

                 modelsArr[dataKey]['stk'] = scrapedData.stk;

            }
        })
    });

    return modelsArr;

} catch (error) {

    console.log("Error", error);
    throw error;
}

}

我的代码- readWriteToFile.js

async function writeToFile(data, filename, type) {

let finalData = '';

if (type == "json") {

    finalData = JSON.stringify(data);

} else if (type == "csv") {

    finalData = arrayToCSV(data);

} else {
    console.log("File type not supported");
    process.exit(1);
}

fs.writeFile("./output/" + type + '/' + filename + '.' + type, finalData, (err) => {
    if (err) {
        console.log(err);
    } else {
        console.log("File written successfully\n");
    }
});

}

我的解决方案

我简单地将所有函数调用包装在异步中，并在前面添加了“等待”。我不工作，也不抛出任何错误。

(async () => {
    
    await scraperA.scrap().then(data => {
            console.log("DATA", data);
            readWriteToFile.writeToFile(data, 'scraped-data-'+timestamp, 'json');
        });
    
    await compare.compareData('./output/json/data.json', './output/json/scraped-data-'+timestamp+'.json').then(data => {
        let dataWithStockData = data;
        mapData = dataWithStock.map( obj => { 
    
            let finalObj = {
                manufacturer: obj.manufacturer,
                grade: obj.condition,
                stock: obj.stock,
            }
            return finalObj;
        });
    });

    await readWriteToFile.writeToFile(mapData, 'data-with-stock-'+timestamp, 'csv');

});

Answer 1

代码结构

(async () => {
    
    /* your code */

});

建议您创建一个异步立即调用函数表达式(IIFE)。但是您必须调用它(最后是())：

(async () => {
    
    /* your code */

})();

使用当前版本的Node.js，您不需要异步生命。Node.js支持顶级等待。

由于readWriteToFile.writeToFile和compare.compareData不返回承诺，所以不能调用.then，而await则没有意义。

从Node.js v14.8开始，您可以编写

await scraperA.scrap().then(data => {
    console.log("DATA", data);
    readWriteToFile.writeToFile(data, 'scraped-data-'+timestamp, 'json');
});

const dataWithStockData = compare.compareData('./output/json/data.json', './output/json/scraped-data-'+timestamp+'.json')
mapData = dataWithStock.map( obj => { 

    let finalObj = {
        manufacturer: obj.manufacturer,
        grade: obj.condition,
        stock: obj.stock,
    }
    return finalObj;
});

readWriteToFile.writeToFile(mapData, 'data-with-stock-'+timestamp, 'csv');

修复问题后，可以考虑使用.then或await / async来清理代码。混合它们通常被认为是糟糕的代码风格。

const data = await scraperA.scrap();
console.log("DATA", data);
readWriteToFile.writeToFile(data, 'scraped-data-'+timestamp, 'json');

const dataWithStockData = compare.compareData('./output/json/data.json', './output/json/scraped-data-'+timestamp+'.json');

mapData = dataWithStock.map( obj => { 

  let finalObj = {
    manufacturer: obj.manufacturer,
    grade: obj.condition,
    stock: obj.stock,
  }
  return finalObj;
});

readWriteToFile.writeToFile(mapData, 'data-with-stock-'+timestamp, 'csv');

Answer 2

如果不知道您调用的哪个函数是同步的还是不同步的，就很难回答。但作出以下假设：

• readWriteToFile.writeToFile返回一个承诺(或者是异步的)
• mapData是在其他地方定义的

你必须：

• 将返回语句添加到第一个.then(...)块的最后一行
• 正如jabaa所说，您必须实际调用该函数。

(async () => {
    
    await scraperA.scrap().then(data => {
            console.log("DATA", data);
            return readWriteToFile.writeToFile(data, 'scraped-data-'+timestamp, 'json');
        });
    
    await compare.compareData('./output/json/data.json', './output/json/scraped-data-'+timestamp+'.json').then(data => {
        let dataWithStockData = data;
        mapData = dataWithStock.map( obj => { 
    
            let finalObj = {
                manufacturer: obj.manufacturer,
                grade: obj.condition,
                stock: obj.stock,
            }
            return finalObj;
        });
    });

    await readWriteToFile.writeToFile(mapData, 'data-with-stock-'+timestamp, 'csv');

})();