function is returning undefined javascript

Question

I wrote a function in javascript expression to check if the result is true or false but i am always getting undefined error

var array = [{
    email: '[email protected]',
    password: '123'
  },
  {
    email: '[email protected]',
    password: '123'
  }
];

let main = function(email, password) {

  return array.forEach((row) => {
    if (row.email === email && row.password === password) {
      return true

    } else {
      return false
    }
  });

};

var checkLogin = main('[email protected]', '123');
console.log(checkLogin)

checkLogin always return undefined

array.forEach doesn't return anything. I think you meant to use map — user47589
– user47589, Commented Dec 10, 2019 at 19:51

Sebastian Kaczmarek · Accepted Answer · 2019-12-10 21:01:47Z

4

It's because forEach does not return anything. You can use simple for-loop, like this:

var array = [
{email: '[email protected]', password: '123'},
{email: '[email protected]', password: '123'}
];

let main = function(email, password) {

    for (var i = 0; i < array.length; i++) {
        var row = array[i];
        if (row.email === email && row.password === password) {
            return true
        }
    }
    return false;
};

var checkLogin = main('[email protected]', '123');
console.log(checkLogin)

Also, take a look at some(), includes(), find() and findIndex()

edited Dec 10, 2019 at 21:01

answered Dec 10, 2019 at 19:52

Sebastian Kaczmarek

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1 Comment

Nina Scholz Over a year ago

btw, this works only with the given array order, but not if the wanted part is the second element of array. you need to move return false to the end of the function, not inside of the for statement, because this ends the iteration with the first element.

sunpietro · Accepted Answer · 2019-12-12 09:12:38Z

2

The forEach array function doesn't return anything. If you touch looped array inside it then you are able to modify existing array without copying it.

edited Dec 12, 2019 at 9:12

answered Dec 10, 2019 at 19:51

sunpietro

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1 Comment

user47589 Over a year ago

It loops over the array. It doesn't necessarily modify anything.

Usman Saleem · Accepted Answer · 2019-12-11 05:10:27Z

1

there's a problem with foreach. it doesn't return anything

var array = [
{email: '[email protected]', password: '123'},
];

let main = function(email, password) {

   for (var i = 0; i < array.length; i++) {
   if (array[i].email === email && array[i].password === password) {
    return true
     } 
       };
      return false
     };

   var checkLogin = main('[email protected]', '123');
   console.log(checkLogin) // returns true

edited Dec 11, 2019 at 5:10

answered Dec 10, 2019 at 20:05

Usman Saleem

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1 Comment

Nina Scholz Over a year ago

btw, this works only with the given array order, but not if the wanted part is the second element of array. you need to move return false to the end of the function, not inside of the for statement, because this ends the iteration with the first element.

Vinayak Shastri · Accepted Answer · 2019-12-10 20:00:15Z

0

there is something wrong with this logic:

return array.forEach((row) => {
if (row.email === email && row.password === password) {
  return true

} else {
  return false
}
});

without this logic it returns anything you want

answered Dec 10, 2019 at 20:00

Vinayak Shastri

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1 Comment

kooskoos Over a year ago

forEach doesn't return anything

Nina Scholz · Accepted Answer · 2019-12-10 20:14:50Z

0

You could take Array#some and return the result of the check.

var array = [{ email: '[email protected]', password: '123' }, { email: '[email protected]', password: '123' }];

let main = (email, password) =>
        array.some(row => row.email === email && row.password === password);

var checkLogin = main('[email protected]', '123');
console.log(checkLogin)

answered Dec 10, 2019 at 20:14

Nina Scholz

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