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 — Bergi
– Bergi, Commented Apr 9, 2014 at 15:35

phylax · Accepted Answer · 2014-04-09 15:59:55Z

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 9, 2014 at 15:59

answered Apr 9, 2014 at 15:30

phylax

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7 Comments

Jo So Over a year ago

I'm not completely sure, but I think that's equivalent to testing newValue[index] != null)

user405398 Over a year ago

undefined === 'undefined' //false

phylax Over a year ago

typeof undefined === 'undefined'

user1943020 Over a year ago

Sorry but this doesn't check the things I need that I mentioned in my question.

user405398 Over a year ago

:D sorry, i didnt notice that!

|

Bergi · Accepted Answer · 2014-04-09 15:40:41Z

0

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;
}

answered Apr 9, 2014 at 15:40

Bergi

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Comments

Easwar Raju · Accepted Answer · 2014-04-09 15:48:12Z

0

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

answered Apr 9, 2014 at 15:48

Easwar Raju

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