1
// 测试对象
2
const emptyObj = {};
3

4
// 1. JSON序列化(由于JSON.stringify自身的序列化策略，所以很不安全)
5
const res1 = JSON.stringify(emptyObj) === "{}";
6
console.log(res1);
7

8
// 2. Reflect
9
const res2 = Reflect.ownKeys(emptyObj).length === 0;
10
console.log(res2);
11

12
// 3. Object.keys()
13
const res3 = Object.keys(emptyObj).length === 0;
14
console.log(res3);
15

16
// 4. Object.getOwnPropertyNames
17
const res4 = Object.getOwnPropertyNames(emptyObj).length === 0;
18
console.log(res4);
19

20
// 5. for...in
21
let res5 = true;
22
for (let key in emptyObj) {
23
  if (Object.prototype.hasOwnProperty.call(emptyObj, key)) {
24
    res5 = false;
25
  }
26
}
27
console.log(res5);
28

29
/**
30
 * 结果：
31
 * 1 true
32
 * 2 true
33
 * 3 true
34
 * 4 true
35
 * 5 true
36
 */

1
// ... 列举其中两种会让JSON.stringify出现异常的例子
2
const obj = {
3
  a: function () {},
4
};
5
const obj2 = {
6
  b: undefined,
7
};
8
console.log(JSON.stringify(obj) === "{}", JSON.stringify(obj2) === "{}"); // true,true   但显然obj和obj2都不是空对象

1
const key = Symbol();
2
const obj = {
3
  [key]: "",
4
};
5
// ...
6
console.log(Object.getOwnPropertyNames(emptyObj).length === 0); // true , 但显然obj并不是一个空对象
7

8
console.log(Reflect.ownKeys(emptyObj).length === 0); // false

1
import getTag from "./.internal/getTag.js";
2
import isArguments from "./isArguments.js";
3
import isArrayLike from "./isArrayLike.js";
4
import isBuffer from "./isBuffer.js";
5
import isPrototype from "./.internal/isPrototype.js";
6
import isTypedArray from "./isTypedArray.js";
7

8
/** Used to check objects for own properties. */
9
const hasOwnProperty = Object.prototype.hasOwnProperty;
10

11
/**
12
 * Checks if `value` is an empty object, collection, map, or set.
13
 *
14
 * Objects are considered empty if they have no own enumerable string keyed
15
 * properties.
16
 *
17
 * Array-like values such as `arguments` objects, arrays, buffers, strings, or
18
 * jQuery-like collections are considered empty if they have a `length` of `0`.
19
 * Similarly, maps and sets are considered empty if they have a `size` of `0`.
20
 *
21
 * @since 0.1.0
22
 * @category Lang
23
 * @param {*} value The value to check.
24
 * @returns {boolean} Returns `true` if `value` is empty, else `false`.
25
 * @example
26
 *
27
 * isEmpty(null)
28
 * // => true
29
 *
30
 * isEmpty(true)
31
 * // => true
32
 *
33
 * isEmpty(1)
34
 * // => true
35
 *
36
 * isEmpty([1, 2, 3])
37
 * // => false
38
 *
39
 * isEmpty('abc')
40
 * // => false
41
 *
42
 * isEmpty({ 'a': 1 })
43
 * // => false
44
 */
45
function isEmpty(value) {
46
  // 处理null的情况
47
  if (value == null) {
48
    return true;
49
  }
50
  // 对于类数组、数组、字符串、arguments对象、buffer等等 使用length属性判断
51
  if (
52
    isArrayLike(value) &&
53
    (Array.isArray(value) ||
54
      typeof value === "string" ||
55
      typeof value.splice === "function" ||
56
      isBuffer(value) ||
57
      isTypedArray(value) ||
58
      isArguments(value))
59
  ) {
60
    return !value.length;
61
  }
62
  // 对于set或map的情况,通过size属性判断
63
  const tag = getTag(value);
64
  if (tag == "[object Map]" || tag == "[object Set]") {
65
    return !value.size;
66
  }
67
  // 具有原型的普通对象
68
  if (isPrototype(value)) {
69
    return !Object.keys(value).length;
70
  }
71
  for (const key in value) {
72
    if (hasOwnProperty.call(value, key)) {
73
      return false;
74
    }
75
  }
76
  return true;
77
}
78

79
export default isEmpty;