How can I reverse an array in JavaScript without using libraries?

Question

I am saving some data in order using arrays, and I want to add a function that the user can reverse the list. I can\'t think of any possible method, so if anybo

Answer 1

Using .pop() method and while loop.

var original = [1,2,3,4];
var reverse = [];
while(original.length){
    reverse.push(original.pop());
}

Output: [4,3,2,1]

Answer 2

You can do

var yourArray = ["first", "second", "third", "...", "etc"]
var reverseArray = yourArray.slice().reverse()

console.log(reverseArray)

You will get

["etc", "...", "third", "second", "first"]

Answer 3

Heres a functional way to do it.

const array = [1,2,3,4,5,6,"taco"];

function reverse(array){
  return array.map((item,idx) => array[array.length-1-idx])
}

Answer 4

Javascript has a reverse() method that you can call in an array

var a = [3,5,7,8];
a.reverse(); // 8 7 5 3

Not sure if that's what you mean by 'libraries you can't use', I'm guessing something to do with practice. If that's the case, you can implement your own version of .reverse()

function reverseArr(input) {
    var ret = new Array;
    for(var i = input.length-1; i >= 0; i--) {
        ret.push(input[i]);
    }
    return ret;
}

var a = [3,5,7,8]
var b = reverseArr(a);

Do note that the built-in .reverse() method operates on the original array, thus you don't need to reassign a.

Answer 5

Here is a version which does not require temp array.

function inplaceReverse(arr) {
  var i = 0;
  while (i < arr.length - 1) {
    arr.splice(i, 0, arr.pop());
    i++;
  }
  return arr;
}

// Useage:
var arr = [1, 2, 3];
console.log(inplaceReverse(arr)); // [3, 2, 1]

Answer 6

53 bytes

function reverse(a){
    for(i=0,j=a.length-1;i<j;)a[i]=a[j]+(a[j--]=a[i++],0)
}

Just for fun, here's an alternative implementation that is faster than the native .reverse method.