Return the index of the last non empty object in javascript

Question

I am trying to get the index of last non empty name in my array of objects. I tried the code below:

var myArray = [{'name':''},{'name':'b'},{'name':''}];
var last = myArray.reduce((acc, curr) => curr ? curr : acc);
console.log(myArray.lastIndexOf(last))

The log always displays 2. The output should be 1 since name == 'b' is not empty. How can I correct this code?

trincot · Accepted Answer · 2021-02-25 17:10:11Z

2

curr is always an object in your case, and objects are always truthy. You should not check for the value of curr, but of curr.name.

var myArray = [{'name':''},{'name':'b'},{'name':''}];
var last = myArray.reduce((acc, curr) => curr.name ? curr : acc);
console.log(myArray.lastIndexOf(last));

You could as an alternative also use reverse and find:

var myArray = [{'name':''},{'name':'b'},{'name':''}];
var last = [...myArray].reverse().find(curr => curr.name);
console.log(myArray.lastIndexOf(last));

answered Feb 25, 2021 at 17:10

trincot

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Comments

adedayojs · Accepted Answer · 2021-03-01 23:19:53Z

1

You could easily use a traditional loop to do that

 var myArray = [{'name':''},{'name':'b'},{'name':''}];
  
  function lastIndex(arr, ppty){
    // Start transversing the array from the rear
    // Improve your time complexity
    for (let i = arr.length - 1; i >= 0; i--) {
      if(arr[i][ppty]){
        return i
      }
    }
    return false // Return false if it's not found
  }

const index = lastIndex(myArray, 'name') // This should give your answer

console.log(index)

edited Mar 1, 2021 at 23:19

answered Feb 25, 2021 at 17:15

adedayojs

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4 Comments

Charlie Wallace Over a year ago

Wouldn't this for (let i = arr.length; i > 0; i--) be for (let i = arr.length-1; i >= 0; i--)

adedayojs Over a year ago

Yes.. I made an error there.. it should be arr.length - 1.. i will update it thanks

Charlie Wallace Over a year ago

you are closer.. but don't you want to go all the way to index zero? for (let i = arr.length-1; i >= 0; i--)

adedayojs Over a year ago

An oversight on my end

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