CODEWITHSUNDEEP
javascript
flix
flix

Reputation: 1974

Javascript - find latest object depending of value

I've tried to find a way to search the latest value of object, and what I found almost all using reverse() or by using i-- in for loop, but I want to avoid it somehow

I can archive it using two var like this:

var a = [{a:true},{a:true},{a:false}]
var b = a.filter(el=>el.a == true)
console.log(b[b.length-1])

Is there a way to use only one var like this?

var a = [{a:true},{a:true},{a:false}]
a.latestValue(el=>el.a == true)

Upvotes: 3

Views: 77

Answers (3)

KATJ Srinath
KATJ Srinath

Reputation: 970

I know already answered but thought it can be achieved in a different way, So here is my solution You can use JavaScript array map function to get the index of latest value like this

NOTE : I have modified your array to contain more elements 

var a = [{a:true},{a:true},{a:false},{a:false},{a:false},{a:true},{a:true},{a:false}];

var latestIndexOfTrue = a.map(function(e) { return e.a; }).lastIndexOf(true)
console.log(latestIndexOfTrue);

  /* above will give you the last index of the value you want (here i have tried with 
  * value true) and it will give you the index as 6 */

if you want whole object then you can get it with bellow code

console.log(a[latestIndexOfTrue]);

Upvotes: 1

CertainPerformance
CertainPerformance

Reputation: 370819

You're basically looking for something like .find, except a .find that starts at the last item and iterates backwards, rather than starting at the first item and iterating forwards. Although there are built-in functions like lastIndexOf (similar to indexOf, except starts searching from the last element) and reduceRight (same, but for reduce), no such thing exists for .find, so your best option is to write your own function. It's easy enough to write, doesn't mutate the original array (like .reverse() does) and doesn't require creating an intermediate array:

function findRight(arr, callback) {
  for (let i = arr.length - 1; i--; i >= 0) {
    if (callback(arr[i], i, arr)) return arr[i];
  }
}

var a = [{id: 1, a:true},{id: 2, a:true},{id: 3, a:false}];
console.log(
  findRight(a, el => el.a === true)
);

I guess it would be possible to (ab)use reduceRight for this, though I wouldn't recommend it:

var a = [{id: 1, a:true},{id: 2, a:true},{id: 3, a:false}];
console.log(
  a.reduceRight((a, el) => a || (el.a && el), null)
);

Upvotes: 1

NoobTW
NoobTW

Reputation: 2564

use find to get only one match.

If you don't like the order, you can reverse it, too.

var a = [{
    a:true,
    id: 1
},{
    a:true,
    id: 2,
},{
    a:false,
    id: 3
}]

const latestValue = a.find(el => el.a === true)
const lastValue = a.reverse().find(el => el.a === true)

console.log(latestValue);
console.log(lastValue);

Upvotes: 2

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