How I take information from within an Array from the index

Question

In this example I already have the numbers of indexes of elements within an Array, but with these numbers I need to get the information out of the Main Array.

This amount of indexes is variable, so it can change at any time.

    IndexNumbers = [ 0, 2 ] // posição das informações na Array

Main Array, from where I need to get the information from the indexes:

    Array= [ 
        {name: "Teste 3", amount: 15000, day: 17},
        {name: "Teste 1", amount: 80000, day: 10},
        {name: "Teste 1", amount: 800000, day: 17}
    ] 

I tried to use the method slice() since it does not alter the Array Principal, but I couldn’t apply it in a way that was what I needed!

The desired return would have to be:

    SliceReturn = [ 
      {name: "Teste 3", amount: 15000, day: 17},
      {name: "Teste 1", amount: 800000, day: 17}
    ] 

Answer 1

You can get this by using a combination of filter, to filter array elements with some, to check if index is in the expected index list:

var indexes = [ 0, 2 ] // posição das informações na Array

var array= [ 
        {name: "Teste 3", amount: 15000, day: 17},
        {name: "Teste 1", amount: 80000, day: 10},
        {name: "Teste 1", amount: 800000, day: 17}
    ];

// o filter irá filtrar os elementos, baseado no .some, que vai identificar se contem algum ("some") elemento dos indexes esperados
var novoArray = array.filter((e,index) => indexes.some(i => index === i));

console.log(novoArray);

Another possibility would be to use the map(), mapping from array the items with the existing index in indexes:

var indexes = [ 0, 2 ] // posição das informações na Array

var array= [ 
        {name: "Teste 3", amount: 15000, day: 17},
        {name: "Teste 1", amount: 80000, day: 10},
        {name: "Teste 1", amount: 800000, day: 17}
    ];

var novoArray = indexes.map((item) => array[item])

console.log(novoArray);

Documentation of filter(), some() and map().

Answer 2

You don’t need slice. If you want another array, then... create another one, and add in it the elements you want.

In this case, just go through the array of positions and insert the respective element in the new array:

var posicoes = [ 0, 2 ]; // posição das informações na Array
var array = [
    { name: "Teste 3", amount: 15000, day: 17 },
    { name: "Teste 1", amount: 80000, day: 10 },
    { name: "Teste 1", amount: 800000, day: 17 }
];

var result = [];
for (var posicao of posicoes) { // para cada posição
    result.push(array[posicao]); // insere o elemento da posição
}

console.log(result);

---

A possible improvement is to check if the position actually exists in the array (because if you access a position that does not exist, a undefined in the final array):

var posicoes = [ 0, 2, 7 ]; // atenção, elemento na posição 7 não existe
var array = [
    { name: "Teste 3", amount: 15000, day: 17 },
    { name: "Teste 1", amount: 80000, day: 10 },
    { name: "Teste 1", amount: 800000, day: 17 }
];

var result = [];
for (var posicao of posicoes) {
    if (0 <= posicao && posicao < array.length) // verifica se o array possui a posição
        result.push(array[posicao]);
}

console.log(result);