Check Object inside an Array using index()

Question

I was solving some challenges of a Javascript course I’m doing, and came across a small problem:

I have the following object array:

var numberObjects = [ 
   {number: 1}, 
   {number: 2}, 
   {number: 3}, 
   {number: 4}, 
   {number: 5}, 
   {number: 6}, 
   {number: 7}, 
   {number: 8}, 
   {number: 9}, 
   {number: 10} 
];

And I need to check for the object {number: 2} within this array, using the method indexOf() and return a message on the console if it is true or false, then I did as follows using the ternary operator:

console.log( numberObjects.indexOf( { number: 2 } ) > -1 ? 'Existe um objeto { number: 2 } em numberObjects!' : 'Não existe um objeto { number: 2 } em numberObjects :(' );

My problem is that even though the object exists { number: 2 } within my array, the return of indexOf() continues to be -1, which means that he is not finding that object within my array, someone would know to inform me why this happens?

I also tried to do by assigning the return of indexOf() a variable, however, without success.

Answer 1

To use index you would need to test if it is the same object. Note that, just because an object has the same keys and values, doesn’t mean that they are the same object. Therefore:

let obj_1 = {number: 1};
let obj_2 = {number: 1};

console.log(obj_1 === obj_2); // false
console.log(obj_1 == obj_2);  // false

To solve your problem you should keep a reference to the objects and use it in index or use the method findIndex to do the same but with a testing function.

Example with index:

let num_1 = {number: 1},
    num_2 = {number: 2},
    num_3 = {number: 3},
    num_4 = {number: 4},
    num_5 = {number: 5};
  
let objetos = [num_1, num_2, num_3, num_4, num_5];

console.log(objetos.indexOf(num_3));  // 2

Example using findIndex:

var objetos = [ 
   {number: 1}, 
   {number: 2}, 
   {number: 3}, 
   {number: 4}, 
   {number: 5}
];

function find_obj(obj) {
    return obj['number'] === 3;
}

console.log(objetos.findIndex(find_obj)); // 2

---

It is also worth remembering that if you are not interested in the index where the object was found, but only want to know if it exists in the array the method includes does it for you.

let num_1 = {number: 1},
    num_2 = {number: 2},
    num_3 = {number: 3},
    num_4 = {number: 4},
    num_5 = {number: 5};
  
let objetos = [num_1, num_2, num_3, num_4, num_5];

console.log(objetos.includes(num_3)); // true

Answer 2

Using index but with map help. But for the value of your object, and not the object. In this case will return 1, the value of the Indice {number:2}.

numberObjects.map((e) => { return e.number; }).indexOf(2);

Answer 3

Good because your function is wrong!

According to the documentation

The index() method returns the first index which has the element found in the array, or -1 if is not present.

Do the test by placing numberObjects.indexof( { number: 20 } ), will give the same answer ie there is no { number : 20 } as value of numberObjects array.

How about using this function?

function verificar(arr, procurar) {
    var chave = procurar[0];
    var valor = procurar[1];
    return !!arr.filter(function (el) {
        return el[chave] == valor;
    }).length;
}

arr is the array:

[ 
   {number: 1}, 
   {number: 2}, 
   {number: 3}, 
   {number: 4}, 
   {number: 5}, 
   {number: 6}, 
   {number: 7}, 
   {number: 8}, 
   {number: 9}, 
   {number: 10} 
]

and search would be the object: {number: 1}

Answer 4

Another way would be to convert the array to string with JSON.stringify() and checking with .indexOf() if you have the object in string form:

var numberObjects = [ 
   {number: 1}, 
   {number: 2}, 
   {number: 3}, 
   {number: 4}, 
   {number: 5}, 
   {number: 6}, 
   {number: 7}, 
   {number: 8}, 
   {number: 9}, 
   {number: 10}
];

var tem = JSON.stringify(numberObjects).indexOf('{"number":2}');

console.log(~tem ? 'Existe um objeto { number: 2 } em numberObjects!' : 'Não existe um objeto { number: 2 } em numberObjects :(');

How objects are in format chave + valor numérico, when converting to string the result will be the quotation key and the numeric value just after the colon:

[{"number":1},{"number":2},{"number":3},{"number":4},{"number":5},{"number":6},{"number":7},{"number":8},{"number":9},{"number":10}]

Then just check if the string {"number":2} exists with .indexOf().

In allocating the .indexOf() to the variable tem, by adding before this variable the ~, will return or 0 (if it does not exist, that is to say false) or any number (positive or negative) indicating that there is.

Now an example that the object does not exist:

var numberObjects = [ 
   {number: 1}, 
   {number: 99}, 
   {number: 3}, 
   {number: 4}, 
   {number: 5}, 
   {number: 6}, 
   {number: 7}, 
   {number: 8}, 
   {number: 9}, 
   {number: 10}, 
   {number: 22} 
];

var tem = JSON.stringify(numberObjects).indexOf('{"number":2}');

console.log(~tem ? 'Existe um objeto { number: 2 } em numberObjects!' : 'Não existe um objeto { number: 2 } em numberObjects :(');