signIn函数总是返回“错误信息”

Question

​

var database = [{
    username: '1',
    password: '2',
  },
  {
    username: '3',
    password: '4',
  },
];
var newsfeed = [{
    username: 'Bobby',
    timeline: 'So tired from all that learning!',
  },
  {
    username: 'Sally',
    timeline: 'Javascript is sooooo cool!',
  },
  {
    username: 'Mitch',
    timeline: 'Javascript is preeetyy cool!',
  },
];


var userNamePrompt = prompt('Enter username:');
var passwordPrompt = prompt('Enter password:');
function signIn(username, password) {
  database.forEach(function (username, password) {
      if (username === database.username && password === database.password) {
        console.log(newsfeed);
      }

      console.log('Wrong information');
    }
  );
}
signIn(userNamePrompt, passwordPrompt);

​

编辑:我怀疑if语句((username === database.username && password === database.password)中的条件由于某些原因总是导致false。

Answer 1

forEach的回调函数返回数据库元素的实例。因此，将其更改为：

​

var databases = [{
    username: '1',
    password: '2',
  },
  {
    username: '3',
    password: '4',
  },
];
var newsfeed = [{
    username: 'Bobby',
    timeline: 'So tired from all that learning!',
  },
  {
    username: 'Sally',
    timeline: 'Javascript is sooooo cool!',
  },
  {
    username: 'Mitch',
    timeline: 'Javascript is preeetyy cool!',
  },
];


var userNamePrompt = prompt('Enter username:');
var passwordPrompt = prompt('Enter password:');
function signIn(username, password) {
  databases.forEach(function (database) {
      if (username === database.username && password === database.password) {
        console.log(newsfeed);
      }
      else{console.log('Wrong information');}

      
    }
  );
}
signIn(userNamePrompt, passwordPrompt);

​

我建议这样做：

​

var databases = [{
    username: '1',
    password: '2',
  },
  {
    username: '3',
    password: '4',
  },
];
var newsfeed = [{
    username: 'Bobby',
    timeline: 'So tired from all that learning!',
  },
  {
    username: 'Sally',
    timeline: 'Javascript is sooooo cool!',
  },
  {
    username: 'Mitch',
    timeline: 'Javascript is preeetyy cool!',
  },
];


var userNamePrompt = prompt('Enter username:');
var passwordPrompt = prompt('Enter password:');
function signIn(username, password) {
  for(let i = 0; i<databases.length;i++){
  const database = databases[i];
      if (username === database.username && password === database.password) {
        console.log(newsfeed);
        return
      }
      
    }
    console.log('Wrong information');
  
}
signIn(userNamePrompt, passwordPrompt);

​

Answer 2

传递给forEach回调的参数不是数据库数组中对象的属性，而是对象本身。

您需要在函数中访问该对象的属性。

database.forEach(function (obj) {
      if (obj.username === database.username && obj.password === database.password) {
        console.log(newsfeed);
      }

      console.log('Wrong information');
    }
  );

Answer 3

我检查了你的原始代码，发现了一些问题。首先，forEach并不像您期望的那样工作。它在每次迭代时将数组的一个元素发送到回调函数。如下所示：

array.forEach( function(elementOfArray) { return ... }

在您的代码中，每个元素都是一个对象，因此可以使用以下命令检查它的值

var database = [{
    username: '1',
    password: '2',
  },
  {
    username: '3',
    password: '4',
  },
];

var userNamePrompt = prompt('Enter username:');
var passwordPrompt = prompt('Enter password:');

function signIn(username, password) {
  var userIsFound = false;
  database.forEach(function (user) {
    if (username === user.username && password === user.password) {
      userIsFound = true;
    };
  })
  if (userIsFound) return 'access granted'
  return 'access denied'
}