javascript - check if object parameter is undefined

Question

I have a situation similar with the one here: Javascript check if object property exists, even when object is undefined.

My problem is, what happens if you have a chain of properties. Example:

var obj = {'a': {'b': {'c': {'d': 'I exists'}}}}

I need to check if 'd' is defined. In order to not get an error, I would have to check like:

if (typeof obj != 'undefined' && typeof obj['a'] != 'undefined' && typeof obj['a']['b'] != 'undefined' && typeof obj['a']['b']['c'] != 'undefined' && typeof obj['a']['b']['c']['d'] != 'undefined')

You can see how this can get annoying. Extrapolate to a level 999 deep element for example. Is there any way to get rid of the first n-1 conditions?

You could surround your obj.a.b.c.d !== 'undefined' statement with a try ... catch block. Like this example. — Phylogenesis
– Phylogenesis, Commented Oct 1, 2015 at 11:21

user2575725 · Accepted Answer · 2015-10-01 11:21:42Z

4

Solution with try-catch:

var check = function(obj) {
  try {
    return (typeof obj.a.b.c.d !== 'undefined');
  } catch (e) {
    return false;
  }
};

alert(check({
  'a': {
    'b': {
      'c': {
        'd': 'I exists'
      }
    }
  }
}));

answered Oct 1, 2015 at 11:21

user2575725

Sign up to request clarification or add additional context in comments.

Comments

Rahul Tripathi · Accepted Answer · 2015-10-01 11:12:53Z

1

You can try like this:

function checkUndefined(obj) {
  var x = Array.prototype.slice.call(arguments, 1);
  for (var i = 0; i < x.length; i++) {
    if (!obj || !obj.hasOwnProperty(x[i])) {
      return false;
    }
    obj = obj[x[i]];
  }
  return true;
}

answered Oct 1, 2015 at 11:12

Rahul Tripathi

173k33 gold badges292 silver badges341 bronze badges

3 Comments

zozo Over a year ago

Was thinking about something similar, hoped I would not need it :).

Rahul Tripathi Over a year ago

You can try to use Tushar's answer as well.

zozo Over a year ago

True, I upvoted it, but that shortens the problem to a certain degree... an object parse solves it.

Community · Accepted Answer · 2017-05-23 12:09:10Z

1

Like Tushar said in his answer:

You can't get rid of the first n - 1 conditions

So you will just have to shorten your statement, so it's not as long.

Check this following example i've created:

JSFIDDLE EXAMPLE

var obj = {'a': {'b': {'c': {'d': 'I exists'}}}};

for (var key in obj)
{
    if (obj && obj.a.b.c.d) 
    { 
        console.log(obj.a.b.c.d);
    }
}

edited May 23, 2017 at 12:09

CommunityBot

11 silver badge

answered Oct 1, 2015 at 11:11

YaBCK

3,0394 gold badges36 silver badges71 bronze badges

Comments

Tushar · Accepted Answer · 2015-10-01 11:20:02Z

1

You can check the value for truthy as follow.

You can't get rid of the first n - 1 conditions but you can shorten your statement

if (obj && obj.a && obj.a.b && obj.a.b.c && typeof obj.a.b.c.d !== 'undefined')
    // Use of obj.a.b.c.d is considered safe here

edited Oct 1, 2015 at 11:20

answered Oct 1, 2015 at 11:08

Tushar

87.4k21 gold badges164 silver badges182 bronze badges

Comments

Oleh Dokuka · Accepted Answer · 2015-10-01 11:22:11Z

Try to write your own property checker like next one:

JavaScript:

function test(object) {
    var restOfKeys = [];
    for (var _i = 1; _i < arguments.length; _i++) {
        restOfKeys[_i - 1] = arguments[_i];
    }
    var propertyToTest;
    if (object === undefined || !restOfKeys.length) {
        return false;
    }
    propertyToTest = restOfKeys.shift();
    if (restOfKeys.length) {
        return test.apply(void 0, [object[propertyToTest]].concat(restOfKeys));
    }
    return object[propertyToTest] !== undefined;
}
var toTest = { a: { b: { c: "asd" } } };
alert(test(toTest, "a", "b", "c"));

TypeScript:

function test(object: any, ...restOfKeys: string[]) {
    let propertyToTest: string;

    if (object === undefined || !restOfKeys.length) {
        return false;
    }

    propertyToTest = restOfKeys.shift();

    if (restOfKeys.length) {
        return test(object[propertyToTest], ...restOfKeys);
    }

    return object[propertyToTest] !== undefined;
}


var toTest = { a: { b: { c: "asd" } } };

alert(test(toTest, "a", "b", "c"));

Source Code here

Black Side · Accepted Answer · 2015-10-01 11:29:52Z

0

var obj = {a:undefined,b:undefined,c:undefined,d:'I exists'};
  if(typeof obj['a'] === 'object'){alert(typeof obj['a']);}
  else if(typeof obj['b'] === 'object'){alert(typeof obj['b']);}
  else if(typeof obj['c'] === 'object'){alert(typeof obj['c']);}
  else{alert(typeof obj['d']+' : '+obj['d']);}

check here http://www.w3schools.com/js/js_datatypes.asp for datatype and here http://www.w3schools.com/js/js_arrays.asp for array.

answered Oct 1, 2015 at 11:29

Black Side

271 bronze badge

Collectives™ on Stack Overflow

javascript - check if object parameter is undefined

6 Answers 6

Comments

3 Comments

Comments

Comments

Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

6 Answers 6

Comments

3 Comments

Comments

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related