將數組作為引用類型node.js

Question

我正在連接到S3並解析出一個json文件，
我創建了一個名為Singer的新對象和一個對象數組。 我想在功能范圍之外使用此對象數組

console.log("Loading up the best code ever!!!");

var fs = require('fs');
// Load the SDK for JavaScript
var AWS = require('aws-sdk');
var jsonfile = require('jsonfile')
var Singer = require('./Singer')
// Set the region 
AWS.config.update({ region: "us-west-1" });
var credentials = new AWS.SharedIniFileCredentials();
AWS.config.credentials = credentials;
// Create S3 service object
s3 = new AWS.S3({ apiVersion: '2006-03-01' });
console.log("after S3");


// Create the parameters for calling createBucket
var bucketParams = {
    Bucket: 'pc-backend-exercises',
    Key: 'toSearch.json',
    ResponseContentType: 'application/json'
};
s3.getObject(bucketParams, function (err, data) {
    // Handle any error and exit
    if (err) {
        console.log(err, err.stack); 
        return err;
    }
    var fileContents = data.Body.toString();
    var json = JSON.parse(fileContents);
    console.log(json);

    var singers = [];
    for (var i = 0; i < json.Search.artists.length; i++) {
        var newSinger = new Singer(json.Search.artists[i]);
        singers.push(newSinger);
    }


    console.log('Singers:');
    console.log(singers);


});

console.log('download json file from s3');

此代碼可以正常工作。 我得到了輸出

Loading up the best code ever!!!
after S3
download json file from s3
{ Search: { artists: [ 'Katy', 'Madonna', 'Rihanna', 'Beyonce' ] } }
Singers:
[ Singer { name: 'Katy', songs: [] },
  Singer { name: 'Madonna', songs: [] },
  Singer { name: 'Rihanna', songs: [] },
  Singer { name: 'Beyonce', songs: [] } ]

但是，我更改代碼以通過引用傳遞數組歌手的方法卻行不通。

var singers = [];
s3.getObject(bucketParams, function (err, data, singers) {
    // Handle any error and exit
    if (err) {
        console.log(err, err.stack); 
        return err;
    }
    var fileContents = data.Body.toString();
    var json = JSON.parse(fileContents);
    console.log(json);


    for (var i = 0; i < json.Search.artists.length; i++) {
        var newSinger = new Singer(json.Search.artists[i]);
        singers.push(newSinger);
    }

});

console.log('Singers:');
console.log(singers);


console.log('download json file from s3');

輸出為：

Loading up the best code ever!!!
after S3
Singers:
[]
download json file from s3
{ Search: { artists: [ 'Katy', 'Madonna', 'Rihanna', 'Beyonce' ] } }
C:\Users\gdarmon\Desktop\Node\node_modules\aws-sdk\lib\request.js:31
            throw err;
            ^

    TypeError: Cannot read property 'push' of undefined
        at Response.<anonymous> (C:\Users\gdarmon\Desktop\Node\gili.js:38:17)
        at Request.<anonymous> (C:\Users\gdarmon\Desktop\Node\node_modules\aws-sdk\lib\request.js:364:18)
        at Request.callListeners (C:\Users\gdarmon\Desktop\Node\node_modules\aws-sdk\lib\sequential_executor.js:105:20)
        at Request.emit (C:\Users\gdarmon\Desktop\Node\node_modules\aws-sdk\lib\sequential_executor.js:77:10)
        at Request.emit (C:\Users\gdarmon\Desktop\Node\node_modules\aws-sdk\lib\request.js:683:14)
        at Request.transition (C:\Users\gdarmon\Desktop\Node\node_modules\aws-sdk\lib\request.js:22:10)
        at AcceptorStateMachine.runTo (C:\Users\gdarmon\Desktop\Node\node_modules\aws-sdk\lib\state_machine.js:14:12)
        at C:\Users\gdarmon\Desktop\Node\node_modules\aws-sdk\lib\state_machine.js:26:10
        at Request.<anonymous> (C:\Users\gdarmon\Desktop\Node\node_modules\aws-sdk\lib\request.js:38:9)
        at Request.<anonymous> (C:\Users\gdarmon\Desktop\Node\node_modules\aws-sdk\lib\request.js:685:12)

你能幫忙嗎？

Answer 1

您在這里有兩個問題。

錯誤訊息

無法讀取未定義的屬性“ push”

看這里：

 s3.getObject(bucketParams, function (err, data, singers) { 

singers是未定義的，因為您定義了一個稱為singers的參數（它將在更大范圍內屏蔽該變量）。 getObject函數在調用傳遞給它的匿名函數時不會給第三個參數賦值。

我不知道你為什么期望它。

如果刪除該參數，則可以再次訪問范圍更廣的singers變量。

執行順序

這是一個常見問題解答。 請參閱如何從異步調用返回響應？ 這可能是所有Stackoverflow上“以重復方式關閉”的前3個目標。

Answer 2

問題是變量的范圍。 您已經在本地和全局中定義了相同的變量名。

更改局部變量的名稱，它應該工作我有變化singers1

var singers = [];
s3.getObject(bucketParams, function (err, data, singers1) {