Reverse function in JavaScript [closed]

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I want to get the reverse of this array, in this case ([4,3,2,1]). The problem is I can use no reverse or other shorcuts.

const ar = [1, 2, 3, 4]

const reverse = function (arr) {


    let x = arr;

        for(i=0; i<x.length;i++) {

        x[x.length-i-1]=x[i];


        }
return x;   
};

const reversedArray = reverse(ar);
console.log(reversedArray);

I thought it must be working, however when I run I get [ 1, 2, 2, 1 ] as an output. Which is because when i=1 at the second index there is no longer 3. What can I do?

run the array up to x.length/2 over two and swap x[i] and x[x.length-i-1] — Kevin L
– Kevin L, Commented Oct 18, 2016 at 15:12
@adeneo the essence of the probelem is to use no helpers, or shortcuts — Erik Hambardzumyan
– Erik Hambardzumyan, Commented Oct 18, 2016 at 15:16

Clyde Lobo · Accepted Answer · 2016-10-18 15:44:49Z

2

It's like swapping two variables without using a temp variable

const ar = [1, 2, 3, 4]

const reverse = function (arr) {


    let x = arr, len = x.length-1;

        for(i=0; i<x.length/2;i++) {

          x[i]+=x[len-i];
          x[len-i]=x[i]-x[len-i];
          x[i]-=x[len-i]


        }
return x;   
};

const reversedArray = reverse(ar);
console.log(reversedArray);

edited Oct 18, 2016 at 15:44

answered Oct 18, 2016 at 15:19

Clyde Lobo

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Comments

Canilho · Accepted Answer · 2016-10-18 15:24:12Z

1

Here is a simple example. But you can achieve the same result with other methods.

function reverse(array){
    var new_array = [];
    for(var i = 0; i< array.length; i++){
        new_array[i] = array[array.length -i - 1];
    }
    return new_array;
}

//how to use
reverse([1,2,3,4,5]); //output

answered Oct 18, 2016 at 15:24

Canilho

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Comments

KevBot · Accepted Answer · 2016-10-18 15:23:18Z

1

You can keep it simple by using a regular for loop, and then just unshifting the values onto a new array:

function reverse(arr) {
  let reversed = [];
  for (let i = 0; i < arr.length; i++) {
    reversed.unshift(arr[i]);
  }
  return reversed;
}


console.log(reverse([1, 2, 3, 4]));
console.log(reverse([6, 7, 8, 9]));

answered Oct 18, 2016 at 15:23

KevBot

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user3589620 · Accepted Answer · 2016-10-18 16:07:15Z

1

With a while loop and starting from the end of the array :

var arr = [1, 2, 3, 4];

function arrReverse(arr) {
  var res = [];
  var max = arr.length - 1;
  while (max > -1) {
    res.push(arr[max]);
    max -= 1;
  }
  return res;
}

var res = arrReverse(arr);
console.log(res);

answered Oct 18, 2016 at 16:07

user3589620

Comments

Bruno Moutinho · Accepted Answer · 2016-10-18 15:20:02Z

0

You're changing the array while you do that because of Javascript's references.

You can use array.prototype.reverse (which is used as [].reverse()) Or you should set a new array and return it.

answered Oct 18, 2016 at 15:20

Bruno Moutinho

616 bronze badges

Comments

Johnnie · Accepted Answer · 2016-10-18 15:15:56Z

-1

Don't use the array as a constant. It is probably not letting you make changes in the array.

Then use the reverse method:

ar.reverse();

answered Oct 18, 2016 at 15:15

Johnnie

1

1 Comment

Mistalis Over a year ago

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