ES6 import/export 合并对象与异步等待

Question

我有两个名为 config.js 和 config.json 的文件，我想将它们合并为一个对象并导出：

config.json

{
  "c": 3
}

config.js

import fs from "fs";
import fse from "fs-extra";
import watch from "node-watch";

const config = {
  a: 1
  b: 2
}

//check does file exists
if (fs.existsSync('./src/config.json')) {
  //event emitter watch for changes in json
  const watcher = watch('./src/config.json', { recursive: true });
  //if json ready, then validate and merge
  watcher.on('ready', async function() {
    const importConfig = await fse.readJson('./src/config.json');
    //merge both default config from current file and json
    Object.assign(config, importConfig)
    //small validate function which checks that `json` can be merged
    const valid = await validationConfig(config)
    if (valid) {
      logger.info('Settings has been valid and imported successfully.');
    } else {
      process.exit(1);
    }
  });
}


//console.log(settings) a & b exists, but c does not
export { config };

但不知何故，即使使用 fs.existsSync export 关键字也不会等待 if 块内的代码结束，而是先于结束。如何解决这个问题？

Answer 1

watcher.on('ready', async function() {

是一个回调。回调下方的同步代码 - 即 export { config } - 将在回调完成前运行。

改为导出一个 Promise，它解析为加载配置的值：

const config = { a: 1, b: 2 };
export const configProm = !fs.existsSync('./src/config.json')
    ? Promise.resolve(config)
    : new Promise((resolve, reject) => { // <----------------------------
        const watcher = watch('./src/config.json', { recursive: true });
        watcher.on('ready', async function () {
            const importConfig = await fse.readJson('./src/config.json');
            Object.assign(config, importConfig)
            const valid = await validationConfig(config)
            if (valid) {
                logger.info('Settings has been valid and imported successfully.');
                resolve(config); // <----------------------------
            } else {
                process.exit(1);
                reject(); // ??
            }
        });
    });

ES6 import/export 合并对象与异步等待

ES6 import/export merge object with async await

javascript

fs

node.js

async-await

es6-modules