这将返回未定义：（节点：3196）UnhandledPromiseRejectionWarning：TypeError：无法读取未定义的属性“myArray”

Posted 2023-03-16

【中文标题】这将返回未定义：（节点：3196）UnhandledPromiseRejectionWarning：TypeError：无法读取未定义的属性“myArray”

【英文标题】：this returns undefined: (node:3196) UnhandledPromiseRejectionWarning: TypeError: Cannot read property 'myArray' of undefined

【发布时间】：2022-01-11 10:37:20

【问题描述】：

这是我的代码：

https://github.com/DavidNyan10/NewProject

const fs = require('fs');
const csv = require('csv-parser')

const myString = new Promise((resolve, reject) => 
    resolve('John');
);

class myClass
    constructor(filename)
        this.myArray = [];
        this.myArray.push(new Promise((res) => 
            fs.createReadStream('filename')
                  .pipe(csv(['FirstName', 'LastName', 'Address', 'Town', 'Country', 'Postcode']))
                  .on('data', (data) => 
                    return(data);
                  )
          ))
    
    async myFunction() 
        for(let i = 0; i < this.myArray.length; i++) 
            if (myString.includes(this.myArray[i]['phrase']))
                if (this.cooled_down(i))
                    this.approve(i, myString);
                
            
        
    
    
    cooled_down(i)
        dictionary = this.myArray[i]
        if (!dictionary.keys().includes('approved'))
            // Means we have never approved on this person!
            return True;
         else
            now = datetime.now();
            duration = now - datetime.fromtimestamp(dictionary['approved']);
            duration_seconds = duration.total_seconds();
            hours = divmod(duration_seconds, 3600)[0];
            if (hours >= 24)
                return True;
             else
                console.log("Couldn't approve " + dictionary['FirstName'] + "Cool Down time: " + 24 - hours);
            
        
        return False;
    

    approve(i, myString)
        dictionary = this.myArray[i];
        try
            setTimeout(function()
                console.log(myString);
                console.log(dictionary['FirstName'])
                console.log(dictionary['Postcode'])
            , 60 * 60 * 3);
        catch(e)
            console.log(e);
        

        now = datetime.now();
        this.myArray[i]['approved'] = now.timestamp();
    


myObj = new myClass("myCSV.csv");
myString.then(myObj.myFunction);

它一直在说

(node:3196) UnhandledPromiseRejectionWarning: TypeError: Cannot read property 'myArray' of undefined
    at myFunction (D:\projects\newproject\index.js:20:30)
    at processTicksAndRejections (internal/process/task_queues.js:95:5)
(Use `node --trace-warnings ...` to show where the warning was created)
(node:3196) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). To terminate the node process on unhandled promise rejection, use the CLI flag `--unhandled-rejections=strict` (see https://nodejs.org/api/cli.html#cli_unhandled_rejections_mode). (rejection id: 2)
(node:3196) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.

但正如您可以清楚地看到的，this.myArray 在第 10 行明确定义。

发生了什么事？

我对 javascript 类和对象还很陌生，所以如果我看起来很笨，我很抱歉。

另外，有什么想法可以让第 11-17 行变得更好吗？我只是将 csv 放入一个数组中，但我不知道这是否是最好的方法。

【参考方案1】：

你打电话给myString.then(myObj.myFunction)。这将 this 关键字从 myObj 更改为其他内容。如果要保留 this 关键字的上下文，则需要手动绑定 this 或调用函数而不是将其传递给 then 回调。示例：

// Binding `this` to object:
myString.then(myObj.myFunction.bind(myObj));

// or
// Calling the function inside anonymous function instead 
// of passing it to `then` callback:
myString.then(() => myObj.myFunction());

【讨论】：

天哪，非常感谢！现在，代码运行没有任何错误，但问题是它没有返回 John 是谁..

@DavidNyan10 你的myString 包含Promise。不是string。您需要将字符串作为参数传递给myFnuction。