Get the last item in an array

Question

Here is my JavaScript code so far:

var linkElement = document.getElementById(\"BackButton\");
var loc_array = document.location.href.split(\'/\');
var newT =         


        

Answer 1

jQuery solves this neatly:

> $([1,2,3]).get(-1)
3
> $([]).get(-1)
undefined

Answer 2

const lastElement = myArray[myArray.length - 1];

This is the best options from performance point of view (~1000 times faster than arr.slice(-1)).

Answer 3

Performance

Today 2020.05.16 I perform tests of chosen solutions on Chrome v81.0, Safari v13.1 and Firefox v76.0 on MacOs High Sierra v10.13.6

Conclusions

• arr[arr.length-1] (D) is recommended as fastest cross-browser solution
• mutable solution arr.pop() (A) and immutable _.last(arr) (L) are fast
• solutions I, J are slow for long strings
• solutions H, K (jQuery) are slowest on all browsers

Details

I test two cases for solutions:

• mutable: A, B, C,

• immutable: D, E, F, G, H, I, J (my),

• immutable from external libraries: K, L, M,

for two cases

• short string - 10 characters - you can run test HERE
• long string - 1M characters - you can run test HERE

function A(arr) {
  return arr.pop();
}

function B(arr) {  
  return arr.splice(-1,1);
}

function C(arr) {  
  return arr.reverse()[0]
}

function D(arr) {
  return arr[arr.length - 1];
}

function E(arr) {
  return arr.slice(-1)[0] ;
}

function F(arr) {
  let [last] = arr.slice(-1);
  return last;
}

function G(arr) {
  return arr.slice(-1).pop();
}

function H(arr) {
  return [...arr].pop();
}

function I(arr) {  
  return arr.reduceRight(a => a);
}

function J(arr) {  
  return arr.find((e,i,a)=> a.length==i+1);
}

function K(arr) {  
  return $(arr).get(-1);
}

function L(arr) {  
  return _.last(arr);
}

function M(arr) {  
  return _.nth(arr, -1);
}






// ----------
// TEST
// ----------

let loc_array=["domain","a","b","c","d","e","f","g","h","file"];

log = (f)=> console.log(`${f.name}: ${f([...loc_array])}`);

[A,B,C,D,E,F,G,H,I,J,K,L,M].forEach(f=> log(f));

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.15/lodash.min.js" integrity="sha256-VeNaFBVDhoX3H+gJ37DpT/nTuZTdjYro9yBruHjVmoQ=" crossorigin="anonymous"></script>

Example results for Chrome for short string

Answer 4

ES6 object destructuring is another way to go.

const {length, [length-1]: last}=[1,2,3,4,5]
console.log(last)

You extract length property from Array using object destructuring. You create another dynamic key using already extracted key by [length-1] and assign it to last, all in one line.

Answer 5

Two options are:

var last = arr[arr.length - 1]

or

var last = arr.slice(-1)[0]

The former is faster, but the latter looks nicer

http://jsperf.com/slice-vs-length-1-arr

Answer 6

if (loc_array[loc_array.length - 1] === 'index.html') {
   // do something
} else {
   // something else
}

In the event that your server serves the same file for "index.html" and "inDEX.htML" you can also use: .toLowerCase().

Though, you might want to consider doing this server-side if possible: it will be cleaner and work for people without JS.