How do I check this boolean hashmap is empty in javascript?

Question

Possible Duplicates:
Object comparison in JavaScript
How do I test for an empty Javascript object from JSON?

var abc = {};
console.log(abc=={}) //false, why?

Why is it false? How do I match a blank hash map...?

{} is a new object. So abc !== "a new object" because abc is another object — mplungjan, Jun 17 '11 at 06:38
@Ikke I think this is not a duplicate of that one. Here we have an interesting point about an empty object. — kapa, Jun 17 '11 at 06:49

mplungjan · Answer 1 · 2020-01-26T18:05:03.253

3

{} is a new object instantiation. So abc !== "a new object" because abc is another object.

This test works:

var abc = {};
var abcd = {
  "no": "I am not empty"
}

function isEmpty(obj) {
  for (var o in obj)
    if (o) return false;
  return true;
}

console.log("abc is empty? " + isEmpty(abc))
console.log("abcd is empty? " + isEmpty(abcd))

Update: Just now saw that several others suggested the same, but using hasOwnProperty

I could not verify a difference in IE8 and Fx4 between mine and theirs but would love to be enlightened

edited Jan 26 '20 at 18:05

answered Jun 17 '11 at 06:40

mplungjan

169,008
28
173
236

1

How does checking the `typeof abc` help with knowing if it is an empty object? – nnnnnn Jun 17 '11 at 06:53
@nnnnnn please see update and other answers testing for properties in the object – mplungjan Jun 17 '11 at 07:59
`hasOwnProperty` is needed to differentiate between properties inherited from the prototype chain (which should not make the object "not empty"), and own properties. When you write a function, you might not want to use it only on `{}` :). – kapa Jun 17 '11 at 09:16

Ravi Parekh · Answer 2 · 2011-06-17T07:14:40.193

1

if (abc.toSource() === "({})")  // then `a` is empty

OR

function isEmpty(abc) {
    for(var prop in abc) {
        if(abc.hasOwnProperty(prop))
            return false;
    }
    return true;
}

edited Jun 17 '11 at 07:14

answered Jun 17 '11 at 07:03

Ravi Parekh

5,253
9
46
58

score 0 · Answer 3 · answered Jun 17 '11 at 06:40

0

var abc = {};

this create an object

so you can try the type of:

if (typeof abc == "object")...

answered Jun 17 '11 at 06:40

Ibu

42,752
13
76
103

score 0 · Answer 4 · answered Jun 17 '11 at 06:51

The statement var abc = {}; creates a new (empty) object and points the variable abc to that object.

The test abc == {} creates a second new (empty) object and checks whether abc points to the same object. Which it doesn't, hence the false.

There is no built-in method (that I know of) to determine whether an object is empty, but you can write your own short function to do it like this:

function isObjectEmpty(ob) {
   for (var prop in ob)
      if (ob.hasOwnProperty(prop))
         return false;

   return true;
}

(The hasOwnProperty() check is to ignore properties in the prototype chain not directly in the object.)

Note: the term 'object' is what you want to use, not 'hash map'.

How do I check this boolean hashmap is empty in javascript?

4 Answers4