How to determine if a Javascript object has only one specific key-value pair?

Question

What would be the easiest way to determine if a Javascript object has only one specific key-value pair?

For example, I need to make sure that the object stored in the variable text only contains the key-value pair 'id' : 'message'

Key-value stores are objects in Javascript. Arrays are a special kind of object with numeric keys. Since you are talking about something with the key `'id'`, you're surely talking about an object rather than an array. — Chuck, Sep 21 '12 at 00:06

score 22 · Accepted Answer · edited Jan 04 '22 at 16:11

22

var keys = Object.keys(text);
var key = keys[0];

if (keys.length !== 1 || key !== "id" || text[key] !== "message")
    alert("Wrong object");

edited Jan 04 '22 at 16:11

Bouke Versteegh

3,280
34
30

answered Sep 21 '12 at 00:16

manager

266
1
2

score 2 · Answer 2 · answered Sep 21 '12 at 02:10

If you are talking about all enumerable properties (i.e. those on the object and its [[Prototype]] chain), you can do:

for (var prop in obj) {

  if (!(prop == 'id' && obj[prop] == 'message')) {
    // do what?
  }
}

If you only want to test enumerable properties on the object itself, then:

for (var prop in obj) {

  if (obj.hasOwnProperty(prop) && !(prop == 'id' && obj[prop] == 'message')) {
    // do what?
  }
}

score 1 · Answer 3 · answered Sep 21 '12 at 00:10

1

var moreThanOneProp = false;
for (var i in text) {
   if (i != 'id' || text[i] != 'message') {
      moreThanOneProp = true;
      break;
   }
}

if (!moreThanOneProp)
   alert('text has only one property');

answered Sep 21 '12 at 00:10

timidboy

1,672
1
16
25

score 1 · Answer 4 · answered Sep 21 '12 at 00:17

If you know the property you want, wouldn't be quicker to just make a shallow copy of the object, pruned of everything is not needed?

var text = {
    id : "message",
    badProperty : "ugougo"
}

text = { id : text.id }

Assuming that I've understood correctly your question...

score 1 · Answer 5 · answered Sep 21 '12 at 00:20

1

you can stringify it and try to match it with a regEx. Example:

if (JSON.stringify(test).match(/\"id":\"message\"/)) {
  console.log("bingo");
}
else  console.log("not found");

answered Sep 21 '12 at 00:20

balafi

2,063
3
16
20

How to determine if a Javascript object has only one specific key-value pair?

5 Answers5

Linked