Object not found within array even though it is

Question

I have 2 object arrays (allUsers and friendsOnTrip). Both these arrays are of the same format. Each object within them contains details of a user (i.e. firstName and lastName). I am trying to make it that if an object in one array is not in the other one, then push that object to a new array, otherwise don't.

allUsers.forEach((user) => {
    if (friendsOnTrip.indexOf(user) <= -1) {
        this._friendsNotOnTrip.push(user);
    }
});

The problem is that even if the object user seems like it is in friendsOnTrip, then the expression of:

if (friendsOnTrip.indexOf(user) <= -1)

...will still evaluate to true (which is wrong) so I end up with objects within this._friendsNotOnTrip that shouldn't be there.

An example of one of the objects:

{
    email: "foo@bar.com",
    firstName: "foo",
    lastName: "bar",
    key: "123456789",
    friends: [
        "987654321",
        "246808642"
    ],
    location: {
        lng: -1.24567,
        lat: 50.9865
    },
    usersToSeeLocation: [
        "987654321"
    ]
}

The object at position 0 in allUsers and the object at position 0 in friendsOnTrip are the same object. I tested the individual attributes and got the following results:

console.log(allUsers[0].firstName === friendsOnTrip[0].firstName);                   //true
console.log(allUsers[0].lastName === friendsOnTrip[0].lastName);                     //true
console.log(allUsers[0].email === friendsOnTrip[0].email);                           //true
console.log(allUsers[0].friends === friendsOnTrip[0].friends);                       //false
console.log(allUsers[0].key === friendsOnTrip[0].key);                               //true
console.log(allUsers[0].location === friendsOnTrip[0].location);                     //false
console.log(allUsers[0].usersToSeeLocation === friendsOnTrip[0].usersToSeeLocation); //false

console.log(allUsers[0] === friendsOnTrip[0]);                                       //false

Looking inside friends, usersToSeeLocation, and location in both allUsers[0] and friendsOnTrip[0], the contents are the exact same so I am unsure as to why those expressions are evaluating to false.

They're not the same object. They hold the same information but they're still deferent object with different space in memory. — ibrahim mahrir, Jan 24 '17 at 12:37
Possible duplicate of [Object comparison in JavaScript](http://stackoverflow.com/questions/1068834/object-comparison-in-javascript) — sabithpocker, Jan 24 '17 at 12:38
Do both the `Objects` have same keys as well as values?? If so then you can try with **JSON.stringify** both the Objects and then compare. If both the `Objects` have same key but having different values then It must be `return` false. — Ashish Panchal, Jan 24 '17 at 12:38
How to tell if two objects are different? What are the keys that only identify one object from the other? — ibrahim mahrir, Jan 24 '17 at 12:39
@Ashish there is no guarantee the keys have the same order, so JSON.stringify comparisons are unstable — fafl, Jan 24 '17 at 12:40
@fafl : Yes It will work only if both the objects have same key value pair. — Ashish Panchal, Jan 24 '17 at 12:45
@Ashish {a:1, b:2} might become "{b:2, a:1}" after stringify — fafl, Jan 24 '17 at 12:50
@fafl : I don't think so that would be the case you can try. :) — Ashish Panchal, Jan 24 '17 at 12:52

score 3 · Accepted Answer · answered Jan 24 '17 at 12:39

3

You can't compare objects like this. For example

[{a: 1, b:2}].indexOf({a: 1, b:2})

returns -1. Instead you should search for a specific property, something like

allUsers.forEach((user) => {
    if (friendsOnTrip.map(u => u.key).indexOf(user.key) <= -1) {
        this._friendsNotOnTrip.push(user);
    }
});

answered Jan 24 '17 at 12:39

fafl

7,222
3
27
50

possibly, the email. – ibrahim mahrir Jan 24 '17 at 12:45
you could also create a string of multiple properties by concatenating them – fafl Jan 24 '17 at 12:49
This has worked, thank you! I had completely forgotten about using `.map()` – wmash Jan 24 '17 at 12:54

Fanyo SILIADIN · Answer 2 · 2017-01-24T12:47:07.887

"Looking inside friends, usersToSeeLocation, and location in both allUsers[0] and friendsOnTrip[0], the contents are the exact same so I am unsure as to why those expressions are evaluating to false."

that's because they are not the same. The have the same value BUT they are not the same object! that's why your "===" returns false You have to compare all indexes one by one

you can do array1.join() === array2.join() to do your comparition faster

Object not found within array even though it is

2 Answers2