Node.js 8.9.3中模块导出Promise结果跨文件访问异常

Hey there, let's fix that frustrating undefined data issue and the TypeError you're hitting—this is all about properly handling Promises and matching Node.js 8.9.3's module behavior. Let's break it down step by step.

First, the root cause #

Your module is probably either not returning the Promise from request-promise at all, or failing to pass the resolved data through the Promise chain. When you import it, you're trying to access data before the Promise resolves, or the module isn't giving you a Promise to wait on in the first place.

Step 1: Fix your module.js to properly return the Promise #

Let's start with the module itself. You need to make sure it exports a function that returns the request-promise Promise, and passes along the resolved data (and re-throws errors so the caller can handle them).

Here are two solid approaches for Node.js 8.9.3 (which supports async/await, by the way):

Option 1: Using .then() chains

const rp = require('request-promise');

// Export a function that returns the Promise
module.exports = function fetchTargetData() {
  return rp('https://your-target-api-url.com')
    .then(data => {
      console.log('Fetched data in module:', data); // Your working console log
      return data; // Critical: pass the data to the next link in the Promise chain
    })
    .catch(err => {
      console.error('Request failed in module:', err);
      throw err; // Re-throw the error so the caller can catch it
    });
};

Option 2: Cleaner async/await syntax

const rp = require('request-promise');

// Async functions automatically return a Promise
module.exports = async function fetchTargetData() {
  try {
    const data = await rp('https://your-target-api-url.com');
    console.log('Fetched data in module:', data);
    return data; // Return the data to resolve the Promise
  } catch (err) {
    console.error('Request failed in module:', err);
    throw err; // Let the caller handle the error
  }
};

Step 2: Correctly use the module in app.js #

Node.js 8.9.3 has experimental support for ES modules (import/export), but it's far more reliable to use CommonJS (require) here (since request-promise is a CommonJS module). The key rule: you can't get the data synchronously—you have to wait for the Promise to resolve with either .then() or async/await.

Option 1: Using .then() in app.js

const fetchTargetData = require('./module.js');

// Wait for the Promise to resolve
fetchTargetData()
  .then(data => {
    console.log('Received data in app.js:', data); // Now this will work!
    // Do what you need with the data here
  })
  .catch(err => {
    console.error('Error in app.js:', err);
  });

Option 2: Using async/await in app.js

Just remember: await can only be used inside an async function.

const fetchTargetData = require('./module.js');

// Wrap your code in an async function
async function main() {
  try {
    const data = await fetchTargetData();
    console.log('Received data in app.js:', data);
    // Use your data here
  } catch (err) {
    console.error('Error in app.js:', err);
  }
}

// Call the async function
main();

Why you were getting TypeErrors #

If you tried something like const data = fetchTargetData(); and then tried to access data.someProperty, you were trying to access properties on a pending Promise object, not the resolved data. That's exactly what causes the TypeError—Promises are objects, not the raw data until they resolve.

Quick note on using import in Node.js 8.9.3 #

If you really want to use import instead of require, you need to:

1. Rename your files to use the .mjs extension (e.g., module.mjs, app.mjs)
2. Run Node with the experimental flag: node --experimental-modules app.mjs
3. Import request-promise like this: import rp from 'request-promise';

But honestly, for Node.js 8.x, sticking with CommonJS (require) is less error-prone.

内容的提问来源于stack exchange，提问作者alexzedim