javascript - 调用包含 promise 链的函数

Question

我有一段代码调用JS函数(NodeJS)。它调用的函数包含一个Promise链。这是调用该函数的代码:

'use strict'

const request = require('request')

try {
  const data = search('javascript')
  console.log('query complete')
  console.log(data)
} catch(err) {
  console.log(err)
} finally {
  console.log('all done')
}

function search(query) {
  searchByString(query).then( data => {
    console.log('query complete')
    //console.log(JSON.stringify(data, null, 2))
    return data
  }).catch( err => {
    console.log('ERROR')
    console.log(err)
    throw new Error(err.message)
  })
}

function searchByString(query) {
  return new Promise( (resolve, reject) => {
    const url = `https://www.googleapis.com/books/v1/volumes?maxResults=40&fields=items(id,volumeInfo(title))&q=${query}`
    request.get(url, (err, res, body) => {
      if (err) {
        reject(Error('failed to make API call'))
      }
      const data = JSON.parse(body)
      resolve(data)
    })
  })
}

当我运行代码时，控制台将显示 query complete，然后显示搜索结果。

然后我得到一个错误: TypeError: google.searchByString(...).then(...).error is not a function这没有任何意义!为什么会触发此错误？

Answer 1

好吧，您正在将返回值分配给数据，但没有返回 promise 的结果!

这是为您提供的可行解决方案，我唯一要做的就是a)在搜索中返回 promise ，b)从已解决的 promise 中获取数据。

您可以在以下位置查看此代码并进行操作:https://runkit.com/arthur/5827b17b8795960014335852

'use strict'

const request = require('request')

try {
  search('javascript')
    .then(
      data => console.log('and the data', data),
      error => console.error('uh - oh', error)
    );
    console.log('the query isn\'t done yet!');
} catch(err) {
  console.error(err);
} finally {
  console.log('all done, or is it?')
}

function search(query) {
  return searchByString(query).then( data => {
    console.log('query complete')
    //console.log(JSON.stringify(data, null, 2))
    return data
  }).catch( err => {
    console.log('ERROR')
    console.log(err)
    throw new Error(err.message)
  })
}

function searchByString(query) {
  return new Promise( (resolve, reject) => {
    const url = `https://www.googleapis.com/books/v1/volumes?maxResults=40&fields=items(id,volumeInfo(title))&q=${query}`
    request.get(url, (err, res, body) => {
      if (err) {
        reject(Error('failed to make API call'))
      }
      const data = JSON.parse(body)
      resolve(data)
    })
  })
}

以下是我从头开始的方法。我认为我在这里最大的改进是使用了节点url lib。这样做总是一件好事，这样可以为您处理字符串转义。在这种情况下，如果用户要输入类似“do n't”的字符串，则可能会中断:)。

require('request');
// request promise is a popular, well tested lib wrapping request in a promise
const request = require('request-promise');
// i like to use url handling libs, they do good things like escape string input.
const url = require('url');

class Search {
    constructor(query) {
        this.query = query;
    }

    fetch() {
        const endpoint = url.parse('https://www.googleapis.com/books/v1/volumes');

        const options = {
            maxResults: 40,
            fields: 'items(id,volumeInfo(title))',
            q: this.query
        }

        endpoint.query = options;

        const callUrl = url.format(endpoint);
        return request.get(callUrl).then(result => JSON.parse(result));
    }
}

const search = new Search('javascript');
search.fetch()
    .then(result => console.log(result))
    .catch(e => console.error('catch:', e));

这是工作代码: https://runkit.com/arthur/5827d5428b24ed0014dcc537