Why Lodash isEmpty Returns True for Integers

In JavaScript, developers often expect Lodash's _.isEmpty function to return false for numbers, assuming that a value like 42 or even 0 represents an existing, non-empty data point. However, _.isEmpty evaluates integers—and all other primitive numbers—as true. This article explains the internal mechanics of _.isEmpty, why numbers are treated as empty, and the proper alternatives to use when validating numeric values.

The Purpose of _.isEmpty

Lodash's _.isEmpty is specifically designed to check the emptiness of collections, not primitive values. It checks whether an enumerable collection (like an Array, Object, Map, or Set) or a sequence (like a String) has any elements or length.

According to Lodash’s documentation, a value is considered empty if it is an empty array, string, arguments object, map, set, or an object with no enumerable string keyed properties.

Why Integers Return true

Under the hood, _.isEmpty executes checks in a specific order:

1. Nullish check: If the value is null or undefined, it returns true.
2. Array-like check: It checks if the value has a valid numeric length property (such as arrays, strings, or NodeLists). Numbers do not have a length property.
3. Map and Set check: It checks if the value has a .size property. Numbers do not have a size property.
4. Object check: It checks whether the value is an object with enumerable own properties using Object.keys() or a similar internal method.

Primitive numbers have no length, no size, and no own enumerable properties. For example:

Object.keys(42); // returns []

Because Object.keys(42) produces an empty list, Lodash sees zero enumerable keys. As a result, Lodash’s fallback mechanism considers the value to have no contents and returns true.

Common Misconception: Truthiness vs. Emptiness

A frequent source of confusion is conflating JavaScript truthiness with collection emptiness. In standard JavaScript:

• Boolean(42) evaluates to true.
• Boolean(0) evaluates to false.

However, _.isEmpty(42) and _.isEmpty(0) both evaluate to true because _.isEmpty does not measure truthiness. It strictly evaluates whether a data container contains items. Numbers are atomic values rather than containers.

How to Correctly Check Numbers

If you need to validate whether an integer or number exists and contains a valid value, avoid _.isEmpty. Instead, use native JavaScript checks or specialized Lodash utilities:

• To check if a value is a valid number:

  typeof value === 'number' && !Number.isNaN(value);
  // Or using Lodash:
  _.isNumber(value) && !_.isNaN(value);

• To check if a value is not null or undefined (including 0):

  value !== null && value !== undefined;
  // Or using Lodash:
  !_.isNil(value);

• To check for finite integers:

  Number.isInteger(value);
  // Or using Lodash:
  _.isInteger(value);

Using the appropriate type-checking function ensures your application handles numeric inputs accurately without falling into the container-based logic of _.isEmpty.