Question

第一次推动自己在一个小型Node项目上使用Ramda，而且我已经遇到了困难。如何用Ramda编写下面的代码？

const dataObject = {};
const promises = [];

for (let i = 0; i < myTableNames.length; i++) {
    const tableName = myTableNames[i];
    const newPromise = new Promise((resolve, reject) => {
        fs.readFile(`./tables/${filename}.json`, (err, content) => {
            if (err) { 
                return reject();
            }
            dataObject[tableName] = JSON.parse(content);
            return resolve();
        });
    });
    promises.push(newPromise);
}

Promise.all(promises).then(() => {
  console.log(dataObject);
});

Answer 1

使用fs-extra：

const fs = require('fs-extra');

const readFile = fileName => fs.readFile(`./tables/${fileName}.json`);
const buildResults = (files) => {
  const build = (acc, json, idx) => R.assoc(myTableNames[idx], JSON.parse(json), acc);
  return R.reduce(build, {}, files);
}

Promise.all(R.map(readFile, myTableNames))
  .then(buildResults)
  .then(data => console.log(data));

Answer 2

如果您使用的是节点v.8，则可以这样做。 Demo

// promisify fs.readFile
const readFile = require('util').promisify(fs.readFile)
const getFilePath = tableName => `./tables/${tableName}.json`
const loadFileContents = pipe(getFilePath, pipeP(readFile, JSON.parse))

// 1. Map each table name into promise that resolves with
//    parsed file content
// 2. Wait for all
// 3. Build object using table names as keys and contents as
//    as values
Promise.all(map(loadFileContents, myTableNames))
  .then(zipObj(myTableNames))
  .then(console.log)

使用Ramda从许多文件中收集JSON数据

2 个答案: