Error while accessing javascript array element inspite of having checks

Question

I am doing following in my javascript code

if(
  typeof player['stats'] != undefined &&
  typeof player['stats']['guild'] != undefined &&
  typeof player['stats']['guild']['master'] != undefined &&
  typeof player['stats']['guild']['master']['since'] != undefined
)

However I get error:

Cannot read property 'since' of null

I have been stuck with this for a while. Can any javascript gurus help me please?

@ibrahimmahrir that did not help :( update: did not see your edit, let me try again — Undefined Variable, Sep 16 '17 at 23:03
@ibrahimmahrir - that worked! you should post that as answer, so I can accept it and others can also be benefitted! — Undefined Variable, Sep 16 '17 at 23:06
Possible duplicate of [How do I check if an object has a property in JavaScript?](https://stackoverflow.com/questions/135448/how-do-i-check-if-an-object-has-a-property-in-javascript) — a-a, Sep 16 '17 at 23:59

Dij · Answer 1 · 2017-09-16T23:05:35.520

1

typeof returns string, so compare against "undefined"

if(
  typeof player['stats'] != "undefined" &&
  typeof player['stats']['guild'] != "undefined" &&
  typeof player['stats']['guild']['master'] != "undefined" &&
  player['stats']['guild']['master'] != null &&
  typeof player['stats']['guild']['master']['since'] != "undefined"
)

edited Sep 16 '17 at 23:05

answered Sep 16 '17 at 22:58

Dij

9,761
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That still won't solve the problem as `player['stats']['guild']['master']` is `null` not `undefined` (deduced from the error).. – ibrahim mahrir Sep 16 '17 at 23:02
@ibrahimmahrir yes missed that, it will need to compare for null too, code corrected, thanks for pointing – Dij Sep 16 '17 at 23:06
@UndefinedVariable check now – Dij Sep 16 '17 at 23:08

ibrahim mahrir · Answer 2 · 2017-09-16T23:11:09.853

1

Just check if the value is truthy:

if(
  player['stats'] &&
  player['stats']['guild'] &&
  player['stats']['guild']['master'] &&
  player['stats']['guild']['master']['since'] != undefined    // only check the last one as it is probably not an object but another value such as 0 (depending on what your data looks like, if you have it as an object then just remove the != undefined check)
)

edited Sep 16 '17 at 23:11

answered Sep 16 '17 at 23:06

ibrahim mahrir

31,174
5
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1

What if `player['stats']['guild']['master']['since']` has _falsy_ value (false , 0 , "" )? – alexmac Sep 16 '17 at 23:08
@alexmac It mostly going to be an object that he is going to use inside the body of `if`. But I've added a check just in case. – ibrahim mahrir Sep 16 '17 at 23:15

score 0 · Answer 3 · answered Sep 16 '17 at 23:57

You could write a fairly simple object getter function which you pass the object and then a dot-delimited key to find a value like so:

function getObj(obj, key) {
  return key.split(".").reduce((acc, cur) => {
    if (acc !== undefined) {
      return acc[cur];
    }
    return acc;
  }, obj);
}

Then, you can grab the value that you want and see if it's undefined or not:

const player = {
  stats: {
    guild: {
      master: {
        since: '2004'
      }
    }
  }
};

const since = getObj(player, 'stats.guild.master.since');
if (since) {
  // do some code
}

This is a handy utility function you can use on any object and makes your if statement much prettier.

I think this will work only if you remove the ` !== undefined` and add it in the if statement `if (since !== undefined)` because in his case master is `null` — Slai, Sep 17 '17 at 00:03
Updated so it gracefully handles null and undefined: https://jsfiddle.net/vhnoqo8u/ — jas7457, Sep 17 '17 at 00:11

score 0 · Answer 4 · answered Sep 17 '17 at 00:00

You can also avoid the multiple lookups with a temporary variable:

player = { stats: { guild: { master: null } } }

if ((temp = player.stats) && 
    (temp = temp.guild)   && 
    (temp = temp.master)  && 
    (temp = temp.since) !== undefined)        
    console.log(true , temp)
else
    console.log(false, temp)


player.stats.guild.master = { since: 'today' }

if ((temp = player.stats) && 
    (temp = temp.guild)   && 
    (temp = temp.master)  && 
    (temp = temp.since) !== undefined)        
    console.log(true , temp)
else
    console.log(false, temp)

Error while accessing javascript array element inspite of having checks

4 Answers4