解构和属性简写错误

Question

我是 node 新手，我正在处理解构。我想从天气 api 的响应中获取 body 属性并对其进行解构。当我连接到互联网时，代码工作正常，但是当我断开互联网时，代码崩溃并抛出错误。

这是我写的代码

```const request = require('request')

const geocode = (address, callback)=>{
    const url = "https://api.mapbox.com/geocoding/v5/mapbox.places/" +encodeURIComponent(address)+ ".json?access_token=theKeyHere"

    request({url, json: true}, (error, {body})=>{
        if(error){
            callback('Uh! Oh, Unable to connect with location service', undefined )
        } else if (body.features.length ===0 || body.message){
            callback(`Uh! Oh, Can't find location. Try another search`, undefined)
        } else {
            callback(undefined, {
                latitude: body.features[0].center[1],
                longitude: body.features[0].center[0],
                location_Name: body.features[0].place_name
            })
        }
    })
}     ```

我得到的错误

    request({url, json: true}, (error, {body={}})=>{
                                        ^

TypeError: Cannot read property 'body' of undefined
    at Request._callback (F:\nodejs\weatherApp\utils\geocode.js:6:41)
    at self.callback (F:\nodejs\weatherApp\node_modules\request\request.js:185:22)
    at Request.emit (events.js:315:20)
    at Request.onRequestError (F:\nodejs\weatherApp\node_modules\request\request.js:877:8)
    at ClientRequest.emit (events.js:315:20)
    at TLSSocket.socketErrorListener (_http_client.js:426:9)
    at TLSSocket.emit (events.js:315:20)
    at emitErrorNT (internal/streams/destroy.js:92:8)
    at emitErrorAndCloseNT (internal/streams/destroy.js:60:3)
    at processTicksAndRejections (internal/process/task_queues.js:84:21)

Answer 1

问题是，当你没有连接到互联网，或者你没有得到预期的响应结构时，该函数的第二个参数是undefined。所以你实际上是在尝试这样做：

undefined.body 当然是错的

你可以做两件事来解决它：

// - this will guarantee that the second argument will always default to 
//   an empty object. this way, you will not get an error
(error, { body={} } = {}) => {

或

(error, response) => {
  let body = {};
  if (response) body = response.body || {};
}

Answer 2

问题在于，当出现错误时，您仍在尝试解构数据：

request({url, json: true}, (error, {body={}})=>{
// −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−^^^^^^^^^^

但是在错误的情况下，数据还没有到达，你得到了undefined。你不能解构undefined 或null。

你有两个选择：

1. 使用一个普通的参数，一旦你知道你没有错误就解构：

    request({url, json: true}, (error, response)=>{
        if (error) {
            // ...
            return;
        }
        const {body = {}} = response;
        // ...
    });
   

2. 为整个参数提供默认值，而不仅仅是body：

    request({url, json: true}, (error, {body={}} = {})=>{
    // −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−^^^^^
        // ...
    });
   

   这样，如果您传递了undefined，您将改为解构{}。并且由于您已经默认 body 如果它在对象上不存在，那么该默认值将生效。