Why can't I use an array as the 'specified condition' in a while loop?

Question

So I have this code:

var myArray = [];

var value = 5;

while (myArray != [5, 4, 3, 2, 1, 0]) {

  myArray.push(value)

  value--;

  console.log(myArray);

}

when I look at the console, it goes on for an infinite loop like so..

[ 5 ]
[ 5, 4 ]
[ 5, 4, 3 ]
[ 5, 4, 3, 2 ]
[ 5, 4, 3, 2, 1 ]
[ 5, 4, 3, 2, 1, 0 ]
[ 5, 4, 3, 2, 1, 0, -1 ]
[ 5, 4, 3, 2, 1, 0, -1, -2 ]
[ 5, 4, 3, 2, 1, 0, -1, -2, -3 ]

..........

Why doesn't it stop at [5,4,3,2,1,0] ? myArray = that at a point and the for loop should stop no?

Sorry for the noob question.

It doesn't work, because two arrays with the same content do not have equal reference in the system - try this in the console `[] === []`. Just use `value > -1` as the condition. — Ori Drori, Apr 17 '20 at 23:07
Thank you @Ori Drori, I didnt know arrays could not equal each other.. When I try that in the console, I see "false". Yes Value > -1 works perfectly. I appreciate the explanation! — Christopher Barreto, Apr 17 '20 at 23:09

score 2 · Accepted Answer · edited Apr 17 '20 at 23:18

JavaScript does not provide built-in support for structural-equality of Arrays, but it's straightforward to implement a comparator:

function arraysEqual(a, b, orderSensitive = true) {
  // Function from https://stackoverflow.com/a/16436975/159145
  // But modified to add the `orderSensitive` option.

  if (a === b) return true;
  if (a == null || b == null) return false;
  if (a.length != b.length) return false;

  if (!orderSensitive) {
    a = Array.from(a).sort();
    b = Array.from(b).sort();
  }

  for (var i = 0; i < a.length; ++i) {
    if (a[i] !== b[i]) return false;
  }
  return true;
}

function yourCode() {
  var myArray = [];
  var value = 5;
  const finalArray = [5, 4, 3, 2, 1, 0];

  while (!arraysEqual(myArray,finalArray)) {
    myArray.push(value)
    value--;
    console.log(myArray);
  }
}

score 0 · Answer 2 · answered Apr 17 '20 at 23:39

you can use the following way to fix the issue if index and values of both arrays are different

while(sortArray(myArray).toString() !== sortArray([5, 4, 3, 2, 1, 0]).toString()) {
// your code
}

sortArray(array) {
  return array.filter((a, b) => a-b)
}

If you are sure the array index and values for both arrays are same you can use

while(myArray.toString() !== [5, 4, 3, 2, 1, 0].toString()) {
// your code
}

score -1 · Answer 3 · answered Apr 17 '20 at 23:34

-1

@Christopher Barreto and welcome to StackOverflow. Good luck with your interesting question.

although @Dai right with his full answer there is much simpler built in a way to convert array to string and then compare them.

That will work for you:

var myArray = [];

var value = 5;

while (myArray.toString() != [5, 4, 3, 2, 1, 0].toString()) {

  myArray.push(value)

  value--;

  console.log(myArray);

}

Or this if you prefer:

while ((''+myArray) != ('' + [5, 4, 3, 2, 1, 0]))

answered Apr 17 '20 at 23:34

pery mimon

7,713
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This is awesome, Thank you Pery. its literally converting the array into a string then comparing the strings. I'll have to add this one to my notes. – Christopher Barreto Apr 18 '20 at 00:01
String conversion is very inefficient though - I strongly recommend _against_ using this in production code, even more-so because the string representation of `[5, 4, 3, 2, 1, 0]` will be regenerated **every** time the `while` loop repeats itself. – Dai Apr 18 '20 at 00:21
Not every code is production code. know how to write quick code is an essential skill. also, this approach used under code in `c `or ` asm` for the conversion. so it much faster then all the `if` in the first answer. – pery mimon Apr 18 '20 at 13:41

Why can't I use an array as the 'specified condition' in a while loop?

3 Answers3