The behavior of JS Array.push may catch you off guard

Question

The behavior of JS Array.push may catch you off guard

There seems to be an issue with the push function in my code. The problem lies in the last line of code shown below.

export enum non_searchFieldsNames {
    language = 'language',
    categories = 'categories',
    subtitle = 'subtitle',
    publishedDate = 'publishedDate',
    id = 'id',
}
enum columnsEnum {
    title,
    authors,
    language,
    categories,
    subtitle,
    publishedDate,
}

function toArray(obj: header | contentCategories | sourceFields) {
    return Object.entries(obj)
        .sort((a, b) => {
            return +a - +b;
        })
        .map(item => item[1]);
}

let sourceFieldsObject: sourceFields = {
    [columnsEnum.title]: searchFieldsNames.title,
    [columnsEnum.authors]: searchFieldsNames.authors,
    [columnsEnum.language]: non_searchFieldsNames.language,
    [columnsEnum.categories]: non_searchFieldsNames.categories,
    [columnsEnum.subtitle]: non_searchFieldsNames.subtitle,
    [columnsEnum.publishedDate]: non_searchFieldsNames.publishedDate,
};

const sourceFieldsArray = toArray(sourceFieldsObject).push(non_searchFieldsNames.id);

The issue arises with the latest line of code. The value returned is 7. When I simplify the code like this:

const sourceFieldsArray = toArray(sourceFieldsObject)

I get an array (minus the additional value). Separating the logic into two lines:

const sourceFieldsArray = (toArray(sourceFieldsObject));
sourceFieldsArray.push(non_searchFieldsNames.id);

Yields the desired outcome. However, I prefer a one-liner solution. What could be causing this error? I also attempted:

const sourceFieldsArray (toArray(sourceFieldsObject)).push(non_searchFieldsNames.id)

Unfortunately, this did not resolve the issue.

javascript arrays

Answer 1

Answer №1

push directly modifies the original array, and instead of returning a new array as anticipated, it provides you with the count of items in that array.

To see push's output value, you can refer to the demonstration below:

const array = [1,1,1] //3 items

const count = array.push(1) //1 additional item

console.log(count) //total of 4 items

If you prefer a concise solution, you may explore the cloning technique using the spread operator

const sourceFieldsArray = [...toArray(sourceFieldsObject), non_searchFieldsNames.id]

Note that this method involves creating an entirely new array, so it's important to be mindful of performance implications when dealing with large arrays.

Answer 2

push directly modifies the original array, and instead of returning a new array as anticipated, it provides you with the count of items in that array.

To see push's output value, you can refer to the demonstration below:

const array = [1,1,1] //3 items

const count = array.push(1) //1 additional item

console.log(count) //total of 4 items

If you prefer a concise solution, you may explore the cloning technique using the spread operator

const sourceFieldsArray = [...toArray(sourceFieldsObject), non_searchFieldsNames.id]

Note that this method involves creating an entirely new array, so it's important to be mindful of performance implications when dealing with large arrays.

The behavior of JS Array.push may catch you off guard

Answer №1

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