Lodash _.tail on Empty Array Behavior

When executing the _.tail method on a strictly empty array ([]) in the Lodash JavaScript library, the function safely returns a new empty array ([]). It does not throw a TypeError, crash, or return null or undefined. This article breaks down the exact mechanics behind this behavior, the underlying implementation, and what developers should expect when working with empty collections in Lodash.

The Return Value

Calling _.tail([]) yields an empty array:

const _ = require('lodash');

const result = _.tail([]);
console.log(result); // Output: []
console.log(Array.isArray(result)); // Output: true
console.log(result.length); // Output: 0

Because _.tail creates a shallow slice of the provided array, the returned empty array is a completely new array instance in memory. Comparing the original empty array to the resulting empty array using strict reference equality (===) evaluates to false.

const input = [];
const output = _.tail(input);

console.log(input === output); // Output: false

How Lodash Implements _.tail

The purpose of _.tail(array) is to retrieve all elements of an array except the first one. Lodash implements this defensively:

1. Length Check: Lodash determines the length of the input collection. For an empty array, the length is 0.
2. Base Slicing: The operation resolves to a slicing logic equivalent to array.slice(1).
3. Empty Bounds: When standard JavaScript slicing is performed on an array where the start index (1) exceeds the array's length (0), the specification dictates that an empty array is returned.

Lodash relies on internal helper functions such as baseSlice to copy elements starting at index 1 up to length. If length is 0, no iterations occur, and an empty array is returned immediately.

Differences from Alternative Methods

Understanding this outcome clarifies how _.tail compares to standard JavaScript patterns:

• Native .slice(1): Running [].slice(1) produces the exact same result ([]).
• Array Destructuring: Running const [, ...rest] = [] also creates an empty array (rest = []).
• Direct Indexing: Attempting to manually grab remaining elements via indices on an empty array can lead to undefined values, whereas _.tail guarantees that the returned value remains an iterable array structure.

Because _.tail([]) safely produces an empty array without runtime errors, it can be seamlessly chained or used in functional pipelines without requiring explicit pre-checks for array length.