Undefined array after push

Question

I'm trying to obtain to sort an array of mountain from the tallest to the smallest but when trying to print, I get

TypeError: mountainArray[i] is undefined

I think i'm not missing any step for the solution but I get undefined.

Thanks in advance

Code below:

var position;
var height;

function Mountain(position, height) {
  this.position = position;
  this.height = height;
}

function sortMountain(a, b) {
  return b.height - a.height;
}

var mountainArray = [];

// game loop
while (true) {
  for (var i = 0; i < 8; i++) {
    var mountainH = parseInt(readline()); // represents the height of one mountain, from 9 to 0.

    mountainArray.push(Mountain(i, mountainH));
    mountainArray.sort(sortMountain);


  }
  for (var i = 0; i < 8; i++) {
    print(mountainArray[i].position);
  }
}

omarjmh · Accepted Answer · 2016-05-22 17:47:49Z

2

The way you have your class written:

function Mountain(position, height) {
  this.position = position;
  this.height = height;
}

You need to use the new keyword when you push:

while (true) {
  for (var i = 0; i < 8; i++) {
    var mountainH = parseInt(readline()); // represents the height of one mountain, from 9 to 0.

    mountainArray.push(new Mountain(i, mountainH)); // HERE
    mountainArray.sort(sortMountain);


  }
  for (var i = 0; i < 8; i++) {
    print(mountainArray[i].position);
  }
}

as pointed out in the comments, you should only sort once, no need to do it every time in your loop.

edited May 22, 2016 at 17:47

answered May 22, 2016 at 17:41

omarjmh

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5 Comments

Telmo Ivo Over a year ago

the readline is called before. the issue was missing the new part from mountainArray.push(new Mountain(i, mountainH)); seems I need to learn JS from the scratch

charlietfl Over a year ago

Also should only sort array once...not each iteration of loop

Scott Sauyet Over a year ago

Note that while the code correctly fixes the error, the text is a little off. new has nothing to do with pushing. You need new because you have a plain constructor function in Mountain, which doesn't return anything if you don't use it with new. You could use push without new if you chose to write Mountain in a different manner.

omarjmh Over a year ago

^^^ I put that in there, right before your comment. thanks

Scott Sauyet Over a year ago

Sure enough. It might be good to note that there are those who find new (and this) horrible features of JS. I'm not one of them, but I do sympathise.

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