Change one property of object

Question

I need to loop through object and change exactly one of its non-true properties to true.

var object = {a: true, b: false, c: false, d: false}

function changeOne(object) {
  for(var i in object) {
    if(object[i] !== true) {
      object[i] = true;
      break;
    }
  }
}

This seems like a really bad way to go about this. Is there a better way?

Possible duplicate of : https://stackoverflow.com/questions/8312459/iterate-through-object-properties — DesTroy, Aug 02 '18 at 17:07

score 1 · Accepted Answer · answered Aug 02 '18 at 17:47

1

Your code is actually fine just that the key order of objects is not defined, so your code might set b or c or d depending on the browsers engine (very unlikely that its not b but you never know...), so you should give an order by yourself:

 function changeOne(object) {
   for(var key of ["a", "b", "c", "d"]) {
     if(object[key] !== true) {
       object[key] = true;
       break;
     }
   }
 }

If you meant "better" in the sense of "shorter":

 const changeOne = obj => ["a", "b", "c", "d"].some(key => (obj[key] !== true) && (obj[key] = true));

answered Aug 02 '18 at 17:47

Jonas Wilms

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does key order even matter to OP? why hard-code object props, OP said they were unpredictable... – dandavis Aug 02 '18 at 18:10
@dandavus no, OP said he doesnt know which proerty exactly is going to change. And yes, keyorder matters. – Jonas Wilms Aug 02 '18 at 18:36

score 1 · Answer 2 · answered Aug 02 '18 at 18:33

You could take the entries of the object and use Array#every for a short circuit after a changed property.

function setToTrue(object) {
    Object.entries(object).every(([k, v]) => v || !(object[k] = true));
    return object;
}

var object = { a: true, b: false, c: false, d: false };

console.log(setToTrue(object));
console.log(setToTrue(object));
console.log(setToTrue(object));

.as-console-wrapper { max-height: 100% !important; top: 0; }

Nir Alfasi · Answer 3 · 2018-08-02T17:53:58.317

0

You can iterate the keys and modify the first one that has a false value:

for (let key of Object.keys(obj)) {
    if (obj[key] !== true) {
        obj[key] = true;
        break;
    }
}

OUTPUT

{ a: true, b: true, c: false, d: false }

Explanation

Object.keys(obj) will get an array of properties defined on the object itself, while var i in object will return additional properties which are part of the prototype. An alternative would be to add a check for obj.hasOwnProperty(key).

edited Aug 02 '18 at 17:53

answered Aug 02 '18 at 17:02

Nir Alfasi

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Do you really think `return` will work here as you expect? – Mamun Aug 02 '18 at 17:07
"No" would've been more concise – snazzybouche Aug 02 '18 at 17:25
@snazzybouche I don't understand your comment, care to explain? – Nir Alfasi Aug 02 '18 at 17:29
@alfasin I asked "Is there a better way of doing this" and your answer is essentially a duplicate of the code in my question - if you could explain why the slight differences in yours make it better, that would be ideal, but otherwise it's pretty much the same – snazzybouche Aug 02 '18 at 17:38
@snazzybouche I just did – Nir Alfasi Aug 02 '18 at 17:38
But arent all the object prototypes props not enumerable? – Jonas Wilms Aug 02 '18 at 17:41
No, it does not. – Jonas Wilms Aug 02 '18 at 17:48
@JonasW. you're right, but I still don't understand your point – Nir Alfasi Aug 02 '18 at 17:49
*the object itself, while var i in object will return additional properties which are part of the prototype* there are none in this case, so your code and the OPs do exactly the same. – Jonas Wilms Aug 02 '18 at 17:50
this seems like a slow (extra array) convoluted way of doing hasOwnProperty without backwards compat, and OP said nothing about mutated protos, which i haven't seen in the wild since JSON took off... – dandavis Aug 02 '18 at 18:08
@dandavis harsh words... do you have a benchmark that shows that running `hasOwnProperty` on each key is so much more performant than calling `Object.keys`? Second, I *did* mention in the answer the option of using `hasOwnProperty`. – Nir Alfasi Aug 02 '18 at 18:49

Change one property of object

3 Answers3