CODEWITHSUNDEEP
javascript
Julius
Julius

Reputation: 1275

Is there something like a filterIndex?

So I am looking for a function like Array.prototype.findIndex which returns an array of indexes. Like Array.prototype.find and Array.prototype.filter return one item and an array of items respectively. I was looking at MDN but couldn't find anything suitable.

I would like to stay compatible with future versions of javascript, is there something planned to be added?

Upvotes: 0

Views: 1181

Answers (4)

weegee
weegee

Reputation: 3409

You can even use .map

var array1 = ['a', 'b', 'a'];
let data = array1.map((data,index) => data == "a" ? index : []).join('').split('')
console.log(data)

You can even just return the index by doing a forEach and return the index if the callback matches.

Array.prototype.filterIndex = function(cb) {
  let arr = [];
  this.forEach((a, index) => {
    if (cb(a)) arr.push(index)
  })
  return arr
}
var array1 = ['a', 'b', 'a'];

let data = array1.filterIndex((data) => data == "a")
console.log(data)

Upvotes: 0

arizafar
arizafar

Reputation: 3122

Why not use existing method Array.prototype.reduce 

let out = ['a','b','a'].reduce((acc, curr, i) => (curr === 'a' && acc.push(i), acc), []);	
console.log(out)

Upvotes: 1

Bergi
Bergi

Reputation: 665130

I guess the most suitable builtin method would be flatMap which you can use for maybe-mapping an array:

['a', 'c', 'a', 'b'].flatMap((v, i) => v == 'a' ? [i] : [])

I am not aware of any proposal to add such a functionality. If you need this more often, you can write your own helper function:

function findIndices(array, callback, ctx) {
    const res = [];
    for (let i=0; i<array.length; i++)
        if (callback.call(ctx, array[i], i, array))
            res.push(i);
    return res;
}


findIndices(['a', 'c', 'a', 'b'], v => v == 'a')

Upvotes: 1

Nina Scholz
Nina Scholz

Reputation: 386746

You could map the indices along with the value and get a callback and return an array of indices.

Array.prototype.filterIndex = function (cb) {
    return this
        .map((o, i) => [o, i])
        .filter(([o]) => cb(o))
        .map(([, i]) => i);
};

console.log(['a', 'b', 'a'].filterIndex(v => v === 'a'));

Upvotes: 1

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