How Lodash _.isArrayBuffer Works and What It Checks

In modern JavaScript development, validating raw binary data structures is essential for data integrity and high-performance processing. This article examines the Lodash utility library's _.isArrayBuffer function, detailing the exact characteristics, internal prototype tags, and environment-specific implementations it uses to confirm whether a given value is a legitimate ArrayBuffer.

1. Object-Like Type Check

Before examining internal descriptors, Lodash performs an isObjectLike check. To meet this criterion, the value must satisfy two basic conditions:

• It must not be null.
• Its typeof evaluation must return 'object'.

This preliminary filter immediately eliminates primitives (such as strings, numbers, booleans, and symbols) and functions from further processing.

2. Internal Tag Matching ([object ArrayBuffer])

In browser and non-Node.js environments, Lodash inspects the internal [[Class]] or [Symbol.toStringTag] metadata of the object. It uses an internal helper (baseGetTag) that mirrors:

Object.prototype.toString.call(value) === '[object ArrayBuffer]';

Lodash specifically looks for the string '[object ArrayBuffer]'. By relying on this tag rather than an instanceof ArrayBuffer operator, the check remains robust across different execution realms (such as iframes or web workers) where prototypes do not share the same memory reference.

3. Node.js Native Type Checking

When running inside a Node.js environment, Lodash optimizes this check by utilizing Node’s native util.types.isArrayBuffer method (historically bound via process.binding('util') or the nodeUtil module). This native C++ binding directly checks the internal layout of the V8 heap object, ensuring maximum speed and preventing false positives caused by objects artificially disguised with custom Symbol.toStringTag properties.

4. Rejection of Views and TypedArrays

A common point of confusion in JavaScript is the difference between an ArrayBuffer and views created on top of one. _.isArrayBuffer strictly verifies the underlying memory buffer, not the view. Consequently, it returns false for:

• TypedArrays: Uint8Array, Int32Array, Float64Array, etc.
• DataView instances: new DataView(buffer)

Even though these structures contain an internal .buffer property pointing to an ArrayBuffer, their internal tags are different (e.g., '[object Uint8Array]' or '[object DataView]'), causing _.isArrayBuffer to reject them.

5. Exclusion of SharedArrayBuffer

Lodash differentiates between standard transferable buffers and shared memory buffers. A SharedArrayBuffer instance returns an internal tag of '[object SharedArrayBuffer]'. Therefore, _.isArrayBuffer evaluates to false when passed a SharedArrayBuffer. Developers needing to accept both must test for shared buffers separately using custom logic or Node's util.types.isSharedArrayBuffer.