How to loop through an array containing objects of objects

Question

This is my array:

[{
    name: "Test",
    skills: {
        agile: true,
        good: true
    }
 },
 {
    name: "Test 2",
    skills: {
        agile: false,
        good: false
    }
 }]

I need to find the last element (his index) who has the skill good set to true. The only way I know to fix this is to use a for/if combination. Is there any other faster/optimal way to do it ?

Answer 1

Use filter:

const goodSkills = myArray.filter(x => x.skills.good)

Then get the last item:

goodSkills[goodSkills.length - 1]

Or if you only need the index, and we treat name as a unique key:

const lastGoodIndex = myArray.findIndex(x => x.name === goodSkills[goodSkills.length - 1].name)

You can then use lastGoodIndex for whatever nefarious purpose you have in mind.

Alternatively if name is not a unique key, I suggest just using forEach :

let lastGoodIndex;
myArray.forEach((x, i) => lastGoodIndex = x.skills.good ? i : lastGoodIndex);
console.log(lastGoodIndex);

Answer 2

The fastest way is to us a for loop:

 var arr = [{ name: "Test", skills: { agile: true, good: true } }, { name: "Test 2", skills: { agile: false, good: false }, }] function findLastGoodIndex(arr) { for (let i = arr.length - 1; i >= 0; i--) { if (arr[i].skills.good) { return i; } } } console.log(findLastGoodIndex(arr)); 

Or if the list isn't that large you can combine reverse with findIndex :

arr.reverse().findIndex(x => x.skills.good));

Answer 3

You can do it in 3 rows:

 var arr = [ { name: "Test", skills: { agile: true, good: true } }, { name: "Test 2", skills: { agile: false, good: false }, } ] var lastIndex; arr.forEach(function(item, i) { if(item.skills.good) lastIndex = i; }) console.log(lastIndex); 

Answer 4

If you want the index of last element that has good = true your best option is to use for/if (perhaps going backwards, ie i-- if you can guess where can you expect the good item?).

filter will find the item(s) too, and it also has index property, but generally it's slower than for/if.

forEach will also generally be slower than for/if .

edit:styling.

Answer 5

Since you need to search the last value, you should search in descending order. This would prevent any unnecessary iterations.

 var data = [{ name: "Test", skills: { agile: true, good: true } }, { name: "Test 2", skills: { agile: false, good: false } } ]; var i = data.length; var result = null; while (i--) { if (data[i].skills.good) { result = i; break; } } console.log(result);