How do I test for an empty JavaScript object?

javascript, javascript-objects

Solution

You can use a for…in loop with an `Object.hasOwn` (ECMA 2022+) test to check whether an object has any own properties:

function isEmpty(obj) {
  for (const prop in obj) {
    if (Object.hasOwn(obj, prop)) {
      return false;
    }
  }

  return true;
}

If you also need to distinguish `{}`-like empty objects from other objects with no own properties (e.g. `Date`s), you can do various (and unfortunately need-specific) type checks:

function isEmptyObject(value) {
  if (value == null) {
    // null or undefined
    return false;
  }

  if (typeof value !== 'object') {
    // boolean, number, string, function, etc.
    return false;
  }

  const proto = Object.getPrototypeOf(value);

  // consider `Object.create(null)`, commonly used as a safe map
  // before `Map` support, an empty object as well as `{}`
  if (proto !== null && proto !== Object.prototype) {
    return false;
  }

  return isEmpty(value);
}

Note that comparing against `Object.prototype` like in this example will fail to recognize cross-realm objects.

Do not use `Object.keys(obj).length`. It is O(N) complexity because it creates an array containing all the property names only to get the length of that array. Iterating over the object accomplishes the same goal but is O(1).

For compatibility with JavaScript engines that don’t support ES 2022+, `const` can be replaced with `var` and `Object.hasOwn` with `Object.prototype.hasOwnProperty.call`:

function isEmpty(obj) {
  for (var prop in obj) {
    if (Object.prototype.hasOwnProperty.call(obj, prop)) {
      return false;
    }
  }

  return true
}

Many popular libraries also provide functions to check for empty objects:

jQuery:

jQuery.isEmptyObject({}); // true

lodash:

_.isEmpty({}); // true

Underscore:

_.isEmpty({}); // true

Hoek:

Hoek.deepEqual({}, {}); // true

ExtJS:

Ext.Object.isEmpty({}); // true

AngularJS (version 1):

angular.equals({}, {}); // true

Ramda:

R.isEmpty({}); // true

Problem

After an AJAX request, sometimes my application may return an empty object, like: ``` var a = {}; ``` How can I check whether that's the case?

Original source

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