Lodash vs Underscore.js: Complete Comparison Guide

Lodash and Underscore.js are both popular JavaScript utility libraries, but Lodash is essentially a superset and more actively maintained version of Underscore.js, offering additional features, better performance optimizations, and improved bundle size management through modern tree-shaking techniques. While Underscore.js was the original library that established the utility pattern, Lodash has evolved to provide more comprehensive functionality, better support for modern JavaScript development practices, and more frequent updates. Both libraries serve similar purposes for functional programming utilities in JavaScript, but your choice may depend on your project’s specific needs regarding bundle size, required features, and long-term maintenance considerations.

Contents

• Core Differences Between Lodash and Underscore.js
• Functionality and API Comparison
• Performance and Bundle Size Considerations
• Modern Development Features
• When to Choose Lodash Over Underscore.js
• When to Choose Underscore.js Over Lodash
• Migration and Interoperability

Core Differences Between Lodash and Underscore.js

Lodash was originally created as a fork of Underscore.js, but it has evolved into a more comprehensive and actively maintained library. The fundamental relationship between these libraries can be understood through several key distinctions:

API Superset Relationship: Lodash’s API is a superset of Underscore.js, meaning that every function available in Underscore.js is also available in Lodash with the same or enhanced functionality source. This makes Lodash a drop-in replacement for Underscore.js in most cases, though with additional capabilities.

Update Frequency and Maintenance: Lodash is updated more frequently than Underscore.js, as noted in multiple sources source. This translates to more bug fixes, security patches, and new features in Lodash over time.

Engineering Discipline: Lodash demonstrates more disciplined engineering practices with semantic versioning and 100% code coverage source. These practices indicate a higher level of quality assurance and predictability for library consumers.

Size and Scope: The libraries differ significantly in their scope - Lodash supports more than 300 chainable helpers, while Underscore maintains a slimmer selection of just over 80 functions source. This makes Underscore.js lighter by default but Lodash more feature-rich.

Functionality and API Comparison

Both libraries provide comprehensive utility functions for JavaScript development, but they have distinct characteristics in their approach and capabilities.

Utility Function Coverage

Common Ground: Both libraries offer similar core functionality including:

• Array manipulation (map, filter, reduce, forEach)
• Object manipulation (extend, clone, merge)
• Function utilities (bind, curry, debounce)
• Collection operations (groupBy, sortBy, countBy)
• String and number utilities

Lodash-Specific Features: Lodash provides several additional functions not found in Underscore.js:

• Deep clone and deep merge capabilities source
• AMD support for better module loading compatibility
• Template pre-compilation utilities for enhanced performance
• More specialized functions like debounce and throttle with additional configuration options

API Design Philosophy

While both libraries promote functional programming paradigms, they differ in their implementation approaches:

Underscore.js: Maintains a more minimalist approach with fewer functions but consistent APIs. It focuses on providing essential utilities without excessive complexity.

Lodash: Offers more comprehensive APIs with additional parameters and options for many functions. For example, Lodash’s _.clone function provides options for deep cloning that Underscore doesn’t offer.

Chaining Support: Both libraries support method chaining, but Lodash’s chaining is often considered more robust and flexible source.

Performance and Bundle Size Considerations

When choosing between these libraries, bundle size and performance optimization become critical factors, especially in modern web applications.

Bundle Size Impact

Default Sizes: Without optimization, Lodash’s comprehensive nature results in a larger default bundle compared to Underscore.js’s minimal approach. This is because Lodash includes over 300 functions while Underscore has around 80.

Tree-Shaking Capabilities: Modern build tools can significantly reduce Lodash’s bundle size through tree-shaking:

• Lodash supports modular imports allowing individual functions to be imported separately
• With proper configuration, Lodash bundles can be reduced to ~30kb (non-gzipped) from much larger sizes source
• Babel plugins can transform lodash imports into more tree-shakeable forms, reducing bundle size by approximately 32kb in some cases source

Optimization Techniques

Modular Imports: Instead of importing the entire library:

// Less optimal for bundle size
import _ from 'lodash';

// Better for tree-shaking
import map from 'lodash/map';
import filter from 'lodash/filter';

Babel Plugin Configuration: Using the Babel plugin for Lodash can implicitly transform recommended imports into per-module imports, significantly reducing the “tree-shaked” bundle size source.

Native Method Comparison: For simple operations, native JavaScript methods may be more performant than either utility library. Modern JavaScript (ES6+) has incorporated many of the functions that were originally provided by these libraries.

Modern Development Features

Lodash has embraced modern JavaScript development practices more aggressively than Underscore.js, making it more attractive for contemporary projects.

ES6 and Module System Support

ES6 Modules: Lodash provides better support for ES6 module syntax and tree-shaking compared to Underscore.js. This is particularly important for modern build tools like Webpack, Rollup, and Vite.

Tooling Integration: Lodash offers better integration with modern development tools and workflows, including improved TypeScript definitions and build-time optimizations.

Performance Optimizations

Lazy Evaluation: Lodash implements lazy evaluation for many operations, which can improve performance in certain scenarios by deferring computation until needed.

Caching: Lodash includes built-in caching mechanisms for frequently used operations, which can provide performance benefits in repeated operations.

Documentation and Community

Active Documentation: Lodash benefits from more active documentation and community resources, making it easier to find solutions to common problems.

TypeScript Support: Lodash generally provides better TypeScript support out of the box, with more comprehensive type definitions and better type inference.

When to Choose Lodash Over Underscore.js

You should prefer Lodash in the following scenarios:

Feature-Rich Applications: When your application requires advanced utility functions beyond what Underscore.js provides, such as deep cloning, advanced merging capabilities, or specialized collection operations.

Bundle Size Optimization: When you’re using modern build tools that can effectively tree-shake Lodash, allowing you to import only the functions you need while maintaining comprehensive functionality.

Long-Term Maintenance: For projects that will benefit from more frequent updates, security patches, and ongoing development effort that Lodash provides.

Modern Development Environments: When working with ES6 modules, TypeScript, or other modern JavaScript features where Lodash’s better tooling integration provides advantages.

Large Codebases: In larger applications where the additional consistency and comprehensive API of Lodash can reduce cognitive overhead and provide more predictable behavior.

When to Choose Underscore.js Over Lodash

Underscore.js may be preferable in certain situations:

Minimal Bundle Requirements: When you need the absolute smallest possible bundle and can’t afford the overhead of tree-shaking configuration, Underscore.js’s smaller default size may be advantageous.

Legacy Codebases: When maintaining older projects that were originally built with Underscore.js and haven’t yet been migrated.

Simplified Dependencies: For projects where you prefer to minimize dependencies and only need basic utility functions that Underscore.js provides.

Educational Purposes: When teaching fundamental JavaScript concepts and you want to avoid the complexity of additional features that Lodash provides.

Niche Environments: In environments with limited tooling or build processes where Lodash’s advanced optimization features can’t be utilized effectively.

Migration and Interoperability

Merging Codebases

Many developers find themselves working with codebases that use one library while preferring the other. Good news: Lodash is designed as a drop-in replacement for Underscore.js, making migration relatively straightforward source.

Interoperability Considerations

Function Compatibility: Most Underscore.js functions work identically in Lodash, though some may have additional options or enhanced behavior.

Chain Compatibility: Method chaining patterns generally work the same way in both libraries, making gradual migration possible.

Migration Strategies

Gradual Migration: You can migrate incrementally by replacing Underscore.js imports with Lodash imports as you encounter them in the codebase.

Bundle Analysis: Use tools like webpack-bundle-analyzer to monitor bundle size changes during migration and optimize imports accordingly.

Testing: Comprehensive testing is recommended during migration to ensure that any behavioral differences between the libraries don’t introduce bugs.

Sources

1. Differences between Lodash and Underscore.js - Stack Overflow
2. Lodash vs Underscore, Differences Between the Popular JavaScript Utility Libraries
3. Underscore vs Lo-Dash
4. Difference between lodash and Underscore - GeeksforGeeks
5. Underscore.js vs Lodash - Which Utility Library is Better for Your JavaScript Projects?
6. Advanced Troubleshooting Guide for Lodash - Mindful Chase
7. How to shrink (tree-shake) lodash in bundle file for React Native?
8. Tree shake Lodash with Webpack, Jest and Typescript
9. Optimization of Lodash styling and bundle size – Technical Notes
10. Why webpack doesn’t tree-shake the lodash when using “import as _”?

Conclusion

Key Takeaways:

• Lodash is a more feature-rich, actively maintained superset of Underscore.js with over 300 functions compared to Underscore’s 80
• Modern build tools can effectively reduce Lodash’s bundle size through tree-shaking, making it competitive with Underscore in optimized applications
• Lodash offers better support for modern JavaScript development practices including ES6 modules, TypeScript, and advanced optimization techniques
• Underscore.js remains viable for minimal bundle requirements or legacy codebases where its smaller default size provides advantages

Action Recommendations:

• New projects: Generally prefer Lodash for its comprehensive features, active maintenance, and modern tooling support
• Bundle-critical applications: Use Lodash with proper tree-shaking configuration rather than defaulting to Underscore.js
• Legacy maintenance: Consider gradual migration from Underscore.js to Lodash when feasible, taking advantage of the drop-in compatibility
• Performance optimization: Always measure actual bundle size and runtime performance in your specific context rather than making assumptions based on library size alone

Related Considerations: For projects where both bundle size and comprehensive functionality are critical, consider exploring modern alternatives like es-toolkit/compat that offer better tree-shaking capabilities while maintaining API compatibility with Lodash source.

Ultimately, the choice between these excellent libraries depends on your specific project requirements, development environment, and long-term maintenance considerations. Both libraries provide exceptional value for JavaScript functional programming utilities.