Iterating in javascript

Question

I am trying to add objects in an array, each array has multiple fields like email and name. The following is how the array looks like. I want to add it to another array.

result = [
  {
    "email": "[email protected]",
    "firstName": "abc"
  },
  {
    "email": "[email protected]",
    "firstName": "def"
  }
]

The following is the logic I'm trying to apply.

var userEmail = ""
var users = [];
var newUser = {'email' : "", 'name' : "", 'type' : 'to'};

for(var i=0; i<result.length; i++){
   userEmail = result[i].email
   //console.log(userEmail);
   newUser.email = result[i].email;
   newUser.name = result[i].firstName; 
   users.push(newUser);
  }

My expected output is this

users = [ { email: '[email protected]', name: 'abc' },
  { email: '[email protected]', name: 'def' } ]

But the output I'm getting is this

[ { email: '[email protected]', name: 'abc' },
  { email: '[email protected]', name: 'abc' } ]

Where am I going wrong?

Alnitak · Accepted Answer · 2016-12-21 11:53:10Z

5

You're repeatedly updating a single object with the new values, instead of creating a new object in each iteration. You should have created var newUser = {}; inside the loop.

That said, it would be better to use .map which is the standard function to transmute an array into another array:

var users = result.map(function(r) {
    return { email: r.email, name: r.firstName, type: 'to' };
});

or in ES6 syntax:

let users = result.map(r => ({ email: r.email, name: r.firstName, type: 'to' }));

edited Dec 21, 2016 at 11:53

answered Dec 21, 2016 at 11:47

Alnitak

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4 Comments

flatbreadcandycane Over a year ago

How do I create a new object in each iteration

Vikrant Over a year ago

that is it! I think, some more description might be required on this.

dotcs Over a year ago

Or by using destructuring: result.map(({email, firstName}) => ({email, name: firstName})). Take away in general is to use the higher order functions (map, filter, reduce, ...) to avoid error prone for iterations when transforming data from one form into another.

Alnitak Over a year ago

@dotcs I'm not sure that the destructuring helps much in this particular case

bbop99 · Accepted Answer · 2016-12-21 11:50:40Z

1

You were running into problems with your newUsers object. Since it is an object you are just adding a reference to this object to the users array. When you are changing it agin in the second iteration you are also mutating the original reference. The below snippet should fix the problem.

var userEmail = ""
var users = [];
                          
for(var i=0; i<result.length; i++){
   users.push({
     email: result[i].email,
     name: result[i].firstName,
     type: 'to'
   });
  }

answered Dec 21, 2016 at 11:50

bbop99

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Comments

Sahadev · Accepted Answer · 2016-12-21 11:57:53Z

-1

Try this:

var result = [
  {
    "email": "[email protected]",
    "firstName": "abc"
  },
  {
    "email": "[email protected]",
    "firstName": "def"
  }
];

users = [];

result.forEach(function(obj){
    var newUser = {};
    newUser.email = obj.email;
    newUser.name = obj.firstName
    users.push(newUser)
})

console.log(users)

answered Dec 21, 2016 at 11:57

Sahadev

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2 Comments

Sahadev Over a year ago

What is wrong with this approch. can anyone explain this ?

Alnitak Over a year ago

you've used .forEach / push when you should have used .map

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