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 = document.createTextNode(unescape(capWords(loc_array[loc_array.length-2]))); 
linkElement.appendChild(newT);

Currently it takes the second to last item in the array from the URL. However I want to do a check for the last item in the array to be "index.html" and if so, grab the third to last item instead.

Answer 1

In ECMAScript proposal Stage 1 there is a suggestion to add an array property that will return the last element: proposal-array-last.

Syntax:

arr.lastItem // get last item
arr.lastItem = 'value' // set last item

arr.lastIndex // get last index

You can use polyfill.

Proposal author: Keith Cirkel(chai autor)

Answer 2

Here's how to get it with no effect on the original ARRAY

a = [1,2,5,6,1,874,98,"abc"];
a.length; //returns 8 elements

If you use pop(), it will modify your array

a.pop();  // will return "abc" AND REMOVES IT from the array 
a.length; // returns 7

But you can use this so it has no effect on the original array:

a.slice(-1).pop(); // will return "abc" won't do modify the array 
                   // because slice creates a new array object 
a.length;          // returns 8; no modification and you've got you last element 

Answer 3

Using lodash _.last(array) Gets the last element of array.

data = [1,2,3]
last = _.last(data)
console.log(last)

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.4/lodash.min.js"></script>

Answer 4

Getting the last item of an array can be achieved by using the slice method with negative values.

You can read more about it here at the bottom.

var fileName = loc_array.slice(-1)[0];
if(fileName.toLowerCase() == "index.html")
{
  //your code...
}

Using pop() will change your array, which is not always a good idea.

Answer 5

I'll suggest to create helper function and reuse it every time, you'll need it. Lets make function more general to be able to get not only last item, but also second from the last and so on.

function last(arr, i) {
    var i = i || 0;
    return arr[arr.length - (1 + i)];
}

Usage is simple

var arr = [1,2,3,4,5];
last(arr);    //5
last(arr, 1); //4
last(arr, 9); //undefined

Now, lets solve the original issue

Grab second to last item form array. If the last item in the loc_array is "index.html" grab the third to last item instead.

Next line does the job

last(loc_array, last(loc_array) === 'index.html' ? 2 : 1);

So, you'll need to rewrite

var newT = document.createTextNode(unescape(capWords(loc_array[loc_array.length-2]))); 

in this way

var newT = document.createTextNode(unescape(capWords(last(loc_array, last(loc_array) === 'index.html' ? 2 : 1)))); 

or use additional variable to increase readability

var nodeName = last(loc_array, last(loc_array) === 'index.html' ? 2 : 1);
var newT = document.createTextNode(unescape(capWords(nodeName)));

Answer 6

I think if you only want get the element without remove, is more simple use this:

arr.slice(-1)

by the way... i didnt check performance, but i think is more simple and clean to write