Return the index of the largest element in an array

Question

I’m trying to return the higher index of the vector, I made the following code but returns undefined in function:

let array = [2, 3, 6, 7, 10, 1];
function retornaMaiorIndice(){
    for (let i = 0; i <= array  ; i++){
        var maior = 0;
        let atual = array[i];
        if (array[i] > atual) {
            maior = array[i];
        }
    } 
    return maior;
}

console.log(retornaMaiorIndice(array));

Answer 1

After many comments, the problem was up to another. As the question had repercussion I will try to give an answer that is what you need.

Need to synchronize the index that is along with the highest value found in another variable, because it is data that needs to be maintained and walk together.

function retornaIndiceMaiorValor() {
    let maior = array[0];
    let indice = 0;
    for (let i = 1; i < array.length; i++) {
        if (array[i] > maior) {
            maior = array[i];
            indice = i;
        }
    }
    return indice;
}

let array = [2, 3, 6, 7, 10, 1];
console.log(retornaIndiceMaiorValor(array));

I put in the Github for future reference.

Note that you can find the index after knowing which is the highest with indexOf(), but then I think it would only be worth it if I used the max() to find the biggest.

To learn the basic errors you had in the original code is the answer below. The question borders to be off topic because he was in need of what he actually needed, he’s the one XY problem, if it is to answer completely, the doubt was about the undefined.

---

The code makes no sense and has several errors.

• The variable initialization must be outside the loop, otherwise the largest will always be 0.
• You must close the loop until i enough in the size of array, and not if iis smaller than thearray, which is not a number, is a complex object with multiple data inside, so take the right property.
• And it should close before it reaches the end because the array starts at zero, it cannot pick up the index that is equal to the size because this index does not exist, it is like having 10 digits, goes from 0 to 9, there is no 10.
• There compares to array[i] is greater than array[i], what is obviously not since it is equal, has no different, perhaps the creation of the unnecessary variable has confused. Interestingly writing right you can read easy because you have to buy with maior even.
• I used 0 to stay in the original rule, but if I allowed negative values then I would have to take the lowest possible negative value or start by taking an initial element to compare. This code works for these numbers, not as a general rule.
• I changed the name of the function to indicate clearly what it does, if I wanted to return the index of the highest value then the name should be retornaIndiceMaiorValor() and then the logic would be different because it would have to control which is the index of the highest value also.
• The rest I improved to simplify and organize.

function retornaMaiorValor() {
    var maior = 0;
    for (let i = 0; i < array.length; i++) if (array[i] > maior) maior = array[i];
    return maior;
}

let array = [2, 3, 6, 7, 10, 1];
console.log(retornaMaiorValor(array));

I put in the Github for future reference.

I considered that this is a case where the person is learning to do so, it is a coding exercise, and as it has several problems in the code it would be important to show how to do the same code, but correctly. In codes in production a simpler and more ready code is more interesting, Augusto demonstrated this form.

Answer 2

To find the highest value within a vector you can use the method Math.max() which returns the greater of one or more numbers:

var lista = [2, 3, 6, 7, 10, 1];
console.log(Math.max.apply(null, lista));

Also possible to do the same code using the scattering syntax that allows an iterable object to be expanded to be used where zero or more arguments are expected:

var lista = [2, 3, 6, 7, 10, 1];
console.log(Math.max(...lista));

Answer 3

Your code has several problems:

• in the for to know the size of the array you need to use array.length:
• you need to start the larger variable just before starting the for;
• you need to see if the current value is greater than the variable maior and not atual.

See how you got these fixes:

let array = [2, 3, 6, 7, 10, 1];
function retornaMaiorIndice() {
    var maior = array[0]
    // iniciando o for com o elemento da posicao 1, pois o maior já é, temporariamente, o da posicao 0
    for (let i = 1; i < array.length; i++){
        if (array[i] > maior) {
            maior = array[i];
        }
    } 
    return maior;
}

console.log(retornaMaiorIndice());