How can I loop through two arrays comparing values in Javascript?

Question

I have the following Javascript function where the parameters newValue and oldValue are arrays of integers and the same length. Any values in these arrays can be an integer, undefined or null:

function (newValue, oldValue) {


});

Is there some way that I could check the values in the arrays one element at a time and then do an action only if:

newValue[index] is >= 0 and < 999
oldValue[index] is >= 0 and < 999
newValue[index] is not equal to oldValue[index]

What I am not sure of is how can I handle in my checks and ignore the cases where newValue or oldValue are not null and not undefined? I know I can do a check as in if (newValue) but then this will show false when it's a 0.

Update:

I had a few quick answers so far but none are checking the right things which I listed above.

possible duplicate of [Detecting an undefined object property in JavaScript](http://stackoverflow.com/questions/27509/detecting-an-undefined-object-property-in-javascript) — Bergi, Apr 09 '14 at 15:35

phylax · Answer 1 · 2014-04-09T15:59:55.510

1

compare against null and undefined:

if (newValue[index] !== null && typeof newValue[index] !== 'undefined') {}

for OPs update:

n = newValue[index];
o = oldValue[index];

if (
  n !== null && typeof n !== 'undefined' && n >= 0 && n < 999 &&
  o !== null && typeof o !== 'undefined' && o >= 0 && o < 999
) {
  // your code
}

for array-elements its not necessary to use typeof so n !== undefined is ok because the variable will exist.

n = newValue[index];
o = oldValue[index];

if (
  n !== null && n !== undefined && n >= 0 && n < 999 &&
  o !== null && o !== undefined && o >= 0 && o < 999 &&
  n !== o
) {
  // your code
}

edited Apr 09 '14 at 15:59

answered Apr 09 '14 at 15:30

phylax

2,034
14
13

1

I'm not completely sure, but I think that's equivalent to testing `newValue[index] != null)` – Jo So Apr 09 '14 at 15:32
undefined === 'undefined' //false – Apr 09 '14 at 15:32
1

typeof undefined === 'undefined' – phylax Apr 09 '14 at 15:33
Sorry but this doesn't check the things I need that I mentioned in my question. – Apr 09 '14 at 15:35
:D sorry, i didnt notice that! – Apr 09 '14 at 15:35
@JoSo `var a = undefined; a != null // false` – phylax Apr 09 '14 at 15:38
@phylax: which would be the intended result – Jo So Apr 09 '14 at 15:50

score 0 · Accepted Answer · answered Apr 09 '14 at 15:40

This will do it:

function isEqual (newValue, oldValue) {
    for (var i=0, l=newValue.length; i<l; i++) {
        if (newValue[i] == null || newValue[i] < 0 || newValue[i] >= 999
         || oldValue[i] == null || oldValue[i] < 0 || oldValue[i] >= 999)
            continue;
        if (newVale[i] !== oldValue[i])
            return false;
    }
    return true;
}

score 0 · Answer 3 · answered Apr 09 '14 at 15:48

0

if (newValue != null || newValue != undefined) && (oldValue != null || oldValue != undefined)

answered Apr 09 '14 at 15:48

Easwar Raju

253
1
4

How can I loop through two arrays comparing values in Javascript?

3 Answers3