> For the complete documentation index, see [llms.txt](https://mm.ricky.moe/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://mm.ricky.moe/javascript/common-js-func/js-empty.md).

# JS  Empty

判断一个变量是否为空

```javascript
isEmpty({a: 3, b: 5}) // false
isEmpty([1, 2]) // false
isEmpty(new Set([1, 2, 2])) // false
isEmpty((new Map()).set('a', 2)) // false
isEmpty({}) // true
isEmpty([]) // true
isEmpty(new Set()) // true
isEmpty(new Map()) // true
isEmpty('abc') // false
isEmpty('') // true
isEmpty(0) // true
isEmpty(1) // true
isEmpty(true) // true
isEmpty(Symbol('abc')); // true
isEmpty(//); // true
isEmpty(new String('abc')); // false
isEmpty(new String('')); // true
isEmpty(new Boolean(true)); // true
isEmpty(null) // true
isEmpty(undefined) // true
```

实现

```javascript
function isEmpty(obj) {
  if (obj == null) {
    return true;
  }

  if (Array.isArray(obj)) {
    return !obj.length;
  }

  if (typeof obj == 'string') {
    return !obj.length;
  }

  var type = {}.toString.call(obj);

  if (type == '[object Object]') {
    return !Object.keys(obj).length;
  }

  if (type == '[object Map]' || type == '[object Set]') {
    return !obj.size;
  }

  // other primitive || unidentifed object type
  return Object(obj) !== obj || !Object.keys(obj).length;
}
```


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