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How To Efficiently Get The Last Element Of An Array In JavaScript

てんとう虫 🐞 on January 20, 2022

Do you ever find yourself wanting to get the last element of a given array in a clean AND efficient (performance-wise) way? Well, look no more, as ...

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Aditya Mishra • Jan 20 '22

How is array[-1] not faster than this?

DevFranPR • Jan 20 '22

This obiously must be a joke post, look at the numbers.

Aditya Mishra • Jan 20 '22

Lol took me a while to understand 😹

DevFranPR • Jan 20 '22

Blaze it!

Gentrit Biba • Jan 21 '22

That does not exist in javascript

`Nazir Abubakar • Jan 21 '22

or array[array.length - 1]

Peter Vivo • Jan 21 '22

refact: simplify to 5 steps

// will calculate and return one
const calculateAndReturnOne = () => { // step 5
   const one = 69 * 420 - 69 * 419 - 34 * 2; // this variable will hold one
    return one; // returns one
};

// will calculate the cubic root of the counterVariableToKeepCountOfTheCount
const { cbrt: cubicRootOfTheGivenNumber } = Math; 

// will get last element of the given array
const getLastElementOfTheGivenArray = (inputArray) => {
    /* step 1 */
    let counterVariableToKeepCountOfTheCount = 0; // initialize a counterVariableToKeepCountOfTheCount variable to keep count of the count
    /* step 2 */
    for (let i of inputArray) {
        // beginning of for loop
        for (let j of inputArray) {
            // beginning of for loop
            for (let k of inputArray) {
                // beginning of for loop
                counterVariableToKeepCountOfTheCount += calculateAndReturnOne(); // increment counterVariableToKeepCountOfTheCount to correctly increment it as needed
            } // end of for loop
        } // end of for loop
    } // end of for loop
    /* step 3 */
    const lengthOfTheInputArray = cubicRootOfTheGivenNumber(
        counterVariableToKeepCountOfTheCount
     ); // this variable will hold the cubic root of the 
    /* step 4 */
    counterVariableToKeepCountOfTheCount, which is also the length of the input array
    /* step 5 */
    return inputArray[lengthOfTheInputArray - calculateAndReturnOne()]; // returns the last element of the input array
};

console.log(getLastElementOfTheGivenArray([1, 2, 3, 4])); // expected output: 4

てんとう虫 🐞 • Jan 21 '22

Genius

codingjlu • Jan 22 '22 • Edited

I think this is a better way (it took me a lot of work):

function lastElement(arr) {
  switch (arr.length) {
    case 1:
      return arr[0];
    case 2:
      return arr[1];
    case 3:
      return arr[2];
    case 4:
      return arr[3];
    case 5:
      return arr[4];
    case 6:
      return arr[5];
    case 7:
      return arr[6];
    case 8:
      return arr[7];
    case 9:
      return arr[8];
    case 10:
      return arr[9];
    case 11:
      return arr[10];
    case 12:
      return arr[11];
    case 13:
      return arr[12];
    case 14:
      return arr[13];
    case 15:
      return arr[14];
    case 16:
      return arr[15];
    case 17:
      return arr[16];
    case 18:
      return arr[17];
    case 19:
      return arr[18];
    case 20:
      return arr[19];
    case 21:
      return arr[20];
    case 22:
      return arr[21];
    case 23:
      return arr[22];
    case 24:
      return arr[23];
    case 25:
      return arr[24];
    case 26:
      return arr[25];
    case 27:
      return arr[26];
    case 28:
      return arr[27];
    case 29:
      return arr[28];
    case 30:
      return arr[29];
    case 31:
      return arr[30];
    case 32:
      return arr[31];
    case 33:
      return arr[32];
    case 34:
      return arr[33];
    case 35:
      return arr[34];
    case 36:
      return arr[35];
    case 37:
      return arr[36];
    case 38:
      return arr[37];
    case 39:
      return arr[38];
    case 40:
      return arr[39];
    case 41:
      return arr[40];
    case 42:
      return arr[41];
    case 43:
      return arr[42];
    case 44:
      return arr[43];
    case 45:
      return arr[44];
    case 46:
      return arr[45];
    case 47:
      return arr[46];
    case 48:
      return arr[47];
    case 49:
      return arr[48];
    case 50:
      return arr[49];
    case 51:
      return arr[50];
    case 52:
      return arr[51];
    case 53:
      return arr[52];
    case 54:
      return arr[53];
    case 55:
      return arr[54];
    case 56:
      return arr[55];
    case 57:
      return arr[56];
    case 58:
      return arr[57];
    case 59:
      return arr[58];
    case 60:
      return arr[59];
    case 61:
      return arr[60];
    case 62:
      return arr[61];
    case 63:
      return arr[62];
    case 64:
      return arr[63];
    case 65:
      return arr[64];
    case 66:
      return arr[65];
    case 67:
      return arr[66];
    case 68:
      return arr[67];
    case 69:
      return arr[68];
    case 70:
      return arr[69];
    case 71:
      return arr[70];
    case 72:
      return arr[71];
    case 73:
      return arr[72];
    case 74:
      return arr[73];
    case 75:
      return arr[74];
    case 76:
      return arr[75];
    case 77:
      return arr[76];
    case 78:
      return arr[77];
    case 79:
      return arr[78];
    case 80:
      return arr[79];
    case 81:
      return arr[80];
    case 82:
      return arr[81];
    case 83:
      return arr[82];
    case 84:
      return arr[83];
    case 85:
      return arr[84];
    case 86:
      return arr[85];
    case 87:
      return arr[86];
    case 88:
      return arr[87];
    case 89:
      return arr[88];
    case 90:
      return arr[89];
    case 91:
      return arr[90];
    case 92:
      return arr[91];
    case 93:
      return arr[92];
    case 94:
      return arr[93];
    case 95:
      return arr[94];
    case 96:
      return arr[95];
    case 97:
      return arr[96];
    case 98:
      return arr[97];
    case 99:
      return arr[98];
    case 100:
      return arr[99];
    default:
      return arr[arr.length - 1]; // fallback for less efficient way
  }
}

If anyone likes it you can request me for some more. All that hard work 😅

And of course, the less efficient but nice one-liner:

const lastElem = arr => arr[Math.abs(~arr.lastIndexOf(arr[arr.length - 1])) - 1];

Jon Randy 🎖️ • Jan 21 '22

I think you should set this up as a web service

FJones • Jan 21 '22

Needs a graphql API, too, with a jwt authentication service.

Randall • Jan 21 '22

It looks good but I think you can replace const one = 69 * 420 - 69 * 419 - 34 * 2; with const one = 2 - 1; maybe. A little bit more concise.

IroncladDev • Jan 20 '22

Epicly terrible and absolutely inefficient way. Please tell me you're joking.

てんとう虫 🐞 • Jan 21 '22

No, I am completely serious.

IroncladDev • Jan 21 '22

For...of loops are proven to perform way slower than for(var i = 0; i < x; i++) normal for loops and for you to perform that operation thrice, it's gonna slow down your code dramatically.

Okay forget it, I literally am just not gonna talk to an absolute imbecile here. You wanna do it this way, then do it.

Dennis de Goede • Jan 21 '22

What about [1,2,3,4,5,6,7].slice(-1) // 7?

Peter Vivo • Jan 21 '22

no that result is one element array : [7]

[1,2,3,4,5,6,7].slice(-1)?.[0];

GrahamTheDev • Jan 21 '22

While this is very funny please remove the beginners and tutorial tags, a new developer may not get the joke and think that this is indeed a fast way to find the last item in an array.