Checking existence of nested property in an object javascript

Question

I have already reviewed some of the answers to similar questions, however, I want to ask my question differently.

Let's say we have a string like "level1.level2.level3. ..." that indicates a nested property in an object called Obj.

The point is that we may not know how many nested properties exist in this string. For instance, it may be "level1.level2" or "level1.level2.level3.level4".

Now, I want to write a function, that given the Obj and the string of properties as input, to simply tell us if such a nested property exists in the object or not (let's say true or false as output).

Update: Thanks to @Silvinus, I found the solution with a minor modification:

        private checkNestedProperty(obj, props) {
        var splitted = props.split('.');
        var temp = obj;
        for (var index in splitted) {
            if (temp[splitted[index]] === 'undefined' || !temp[splitted[index]]) return false;
            temp = temp[splitted[index]];
        }
        return true;
    }

@Pedram, you want to get "report" about existence of each property or just for the most(last) nested one? — RomanPerekhrest, May 04 '16 at 06:39
@RomanPerekhrest In fact, the most (last) one. However, it is obvious that if each of these properties does not exist, the last one does not exist as well :) — Pedram, May 04 '16 at 06:45

Nina Scholz · Answer 1 · 2022-01-22T13:59:03.947

4

You could use Array#every() and thisArg of it, by iterating the keys and checking if it is in the given object.

var fn = function (o, props) {
    return props.split('.').every(k => k in o && (o = o[k], true));
}

console.log(fn({}, "toto.tata"));                                   // false
console.log(fn({ toto: { tata: 17 } }, "toto.tata"));               // true
console.log(fn({ toto: { tata: { tutu: 17 } } }, "toto.foo.tata")); // false
console.log(fn({ toto: { tata: false } }, "toto.tata")); // true

edited Jan 22 '22 at 13:59

answered May 04 '16 at 07:44

Nina Scholz

376,160
25
347
392

1

does not work if value of a key is falsy, or null. `console.log(fn({ toto: { tata: false } }, "toto.tata")); // false` – Morlo Mbakop Jan 22 '22 at 13:54
@MorloMbakop, thank you for the hint. now it should work as expected. please see edit. – Nina Scholz Jan 22 '22 at 13:59
Looks lovely like ost of your answers, although i don't understand it. – Morlo Mbakop Jan 22 '22 at 14:12

Silvinus · Accepted Answer · 2016-05-04T06:49:00.930

3

You can explore your Obj with this function :

var fn = function(obj, props) {
        var splited = props.split('.');
        var temp = obj;
        for(var index in splited) {
            if(typeof temp[splited[index]] === 'undefined') return false;
            temp = temp[splited[index]]
        }
           return true
        }

var result = fn({ }, "toto.tata");
console.log(result); // false

var result = fn({ toto: { tata: 17 } }, "toto.tata");
console.log(result); // true

var result = fn({ toto: { tata: { tutu: 17 } } }, "toto.foo.tata");
console.log(result); // false

This function allow to explore nested property of Obj that depends of props passed in parameter

edited May 04 '16 at 06:49

answered May 04 '16 at 06:21

Silvinus

1,445
8
16

This answer fails on the case `fn({a:false}, 'a')`. Minor point, but there is no need for the variable `temp` here. – May 04 '16 at 06:23
Also, shouldn't it be `temp = temp[splited[index]];`? For that reason, the test case `fn({a: {b: { c: 1 }}}, 'a.b.c')` causes a run-time error "Cannot read property 'c' of undefined". – May 04 '16 at 06:29
For the first comment, ... I agree. I write this code so fast. I edited it and change my test by if(typeof temp[splited[index]] === 'undefined') return false; For the second, sorry it's a mistake. temp = obj[splited[index]] must be replace by temp = temp[splited[index]] – Silvinus May 04 '16 at 06:48
@Silvinus Thank you, I have modified your answer (minor mistake) and put the correct function in my update. – Pedram May 04 '16 at 06:54

score 1 · Answer 3 · edited May 23 '17 at 11:45

1

This answer provides the basic answer to your question. But it needs to be tweaked to handle the undefined case:

function isDefined(obj, path) {
  function index(obj, i) { 
    return obj && typeof obj === 'object' ? obj[i] : undefined; 
  }

  return path.split(".").reduce(index, obj) !== undefined;
}

edited May 23 '17 at 11:45

Community

1
1

answered May 04 '16 at 06:17

why downvote? downvoter, how about some explanation?! Or, maybe, you're just clicking without arguments ? – RomanPerekhrest May 04 '16 at 06:58

Ostn · Answer 4 · 2018-03-03T23:09:10.127

Based on the solution given by @Silvinus here is a solution if you deal with array inside nested objects (as it is often the case in results from databases queries) :

checkNested = function(obj, props) {
    var splited = props.split('.');
    var temp = obj;
    for(var index in splited) {
      var regExp = /\[([^)]+)\]/;
      var matches = regExp.exec(splited[index])
      if(matches) {
        splited[index] = splited[index].replace(matches[0], '');
      }
      if(matches) {
        if(matches && typeof temp[splited[index]][matches[1]] === 'undefined') return false;
            temp = temp[splited[index]][matches[1]];
      }
      else {
            if(!matches && typeof temp[splited[index]] === 'undefined') return false;
                temp = temp[splited[index]]
      }
    }
    return true
}

obj = {ok: {ao: [{},{ok: { aa: ''}}]}}

console.log(checkNested(obj, 'ok.ao[1].ok.aa')) // ==> true
console.log(checkNested(obj, 'ok.ao[0].ok.aa')) // ==> false

Checking existence of nested property in an object javascript

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