Reversing an Array in JavaScript.

Awesome answer, this really helps. However do you know if there is a way to do this without having a temporary empty array? I forgot to mention this as my challenge also mentions this.

How are they expecting you to output information? Can each value of the array be outputted individually or must it appear in a collection? I mean, in order for the code to be outputted to a collection such as an array, it needs to be stored in a temporary container. That data has to have somewhere to go so that it can be re-ordered, whether it's output to the screen in some form or output to a container.

I found a way to do this with a while loop, however it's returning undefined for some reason.

var x = [-3,5,1,3,2,10];


function reverse(a) {

  var first = 0;
  var last = a.length - 1;

  while (first < last) {
    var b = a[first];
    a[first] = a[last];
    a[last] = b;

    first++;
    last++;
  }

}

console.log(reverse(x));

Any ideas?

If you said you can't use a variable to store the array values in, you're violating that rule by using the b variable, but then again, there's no other way to do it without a temporary container such as the b variable.

Functions will always return undefined when there is no defined return value. Also you need to have the last variable subtracting because otherwise the loop is infinite. First can never be less than last if they are both going into positive infinity.

One more thing is that using the loop this way permanently changes the array that is fed into the function. It doesn't just return a copy of the array reversed; it permanently reverses it. This is often not the behavior you want. You'd want to have a copy of the information to do with as you please while preserving the formatting of the original array. I know this is a challenge, but it doesn't seem like a very well made challenge to be honest.

var x = [-3,5,1,3,2,10];


function reverse(a) {

  var first = 0;
  var last = a.length - 1;

  while (first < last) {
    var b = a[first];
    a[first] = a[last];
    a[last] = b;

    first++;
    last--;
  }
return a;
}

console.log(reverse(x));
//shows that x is permanently changed
console.log("x is now: "+x);

Just to give more reason and credence as to why I say this challenge isn't right is to look at the default global JavaScript functions. Let's say "parseInt" for example. You know "parseInt" grabs a number from a string and returns that number. But it does not permanently change the variable that is called into it.

var width = "130px";
console.log(parseInt(width));
console.log(width);

You can notice after running this that width did not change after running parseInt() on it because it preserves the original formatting of the variable called.

Thank you so much for helping me with this challenge. The challenge didn't let me specifically use an empty "array" variable, however the variable that I used was fine according to the challenge that I had received. While I do agree with everything you say here that it is not good programming practice to do it in this way, the whole purpose of the challenge was just to reverse the array and not to create it to use for a long term program. I completely understand that it is bad practice to change an initial value of a variable.