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

This question already has answers here: Closed 11 years ago.

Possible Duplicates:

Object comparison in JavaScript

How do I test for an empty Javascript object from JSON?

var abc 开发者_开发技巧= {};
console.log(abc=={}) //false, why?

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

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{} 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

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

OR

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

---

var abc = {};

this create an object

so you can try the type of:

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

---

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'.