Node.js promisifaction 错误

问题描述

创建一个名为 big.file 的文件并存储值:

Created a file name big.file and stored values:

const fs = require('fs');
const file = fs.createWriteStream('./big.file');

for(let i=0; i<= 2; i++) {
  file.write('1\n2\n3');
}
file.end()

尝试过promisifaction，但我不确定是不是这样.

Tried promisifaction, but I am not sure is this way or not.

function readFile('./big.file','utf8'){
    return new Promise(function(resolve,reject){
        fs.readFile('./big.file', 'utf8',function(err,data){
            if(err) reject (err);
            else{
                console.log(data);
                const lines =data.split('\n');
                console.log(lines);
                const numbers = lines.map(Number);
                const oddNumbers = numbers.filter(n => n%2 === 1);
                console.log('Odd numbers count:', oddNumbers.length);
            }
        });
    });
};

推荐答案

当没有错误时，您需要使用数据调用 resolve 回调.

You need to call resolve callback with the data, when there is no error.

function readFile(filename, encoding) {
    return new Promise(function(resolve, reject) {
        fs.readFile(filename, encoding, function(err, data) {
            if (err) {
              return reject (err);
            }
            console.log(data);
            const lines =data.split('\n');
            console.log(lines);
            const numbers = lines.map(Number);
            const oddNumbers = numbers.filter(n => n%2 === 1);
            console.log('Odd numbers count:', oddNumbers.length);
            resolve(oddNumbers);
        });
    });
};

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