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

It can also be achieved using map method.

[1, 2, 3].map((value, index, arr) => arr[arr.length - index - 1])); // [3, 2, 1]

Or using reduce (little longer approach)

[1, 2, 3].reduce((acc, curr, index, arr) => {
    acc[arr.length - index - 1] = curr;
    return acc;
}, []);

Answer 2

This function will work with arrays that have may have gaps between their indices.

function reverse( a ) {
    var b = [], c = [] ;
    a.forEach( function( v ) { b.push( v ) } ) ;
    a.forEach( function( v, i ) { c[i] = b.pop() } ) ;
    return c ;
}

var a= [] ; a[1] = 2 ; a[3] = 4 ; a[7] = 6 ; a[9] = 8 ;
a = reverse( a ) ;
var s = '' ;
a.forEach( function( v, i ) { s += 'a[' + i + '] = ' + v + '  ' } ) ;
console.log( s ) ;
// a[1] = 8  a[3] = 6  a[7] = 4  a[9] = 2

Answer 3

reveresed = [...array].reverse()

Answer 4

reverse array and sub-array (in place) with ES6.

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

Answer 5

reverse in place with variable swapping (mutative)

const myArr = ["a", "b", "c", "d"];
for (let i = 0; i < (myArr.length - 1) / 2; i++) {  
    const lastIndex = myArr.length - 1 - i; 
    [myArr[i], myArr[lastIndex]] = [myArr[lastIndex], myArr[i]] 
}

Answer 6

We have reverse() function to reverse the given array in JS.

var a = [7,8,9];
a.reverse(); // 9 8 7

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