es-toolkit: How a Small Internal Library Became a Global Project (opens in new tab)
es-toolkit began at Toss as a modern alternative to lodash, addressing its outdated architecture, legacy-browser code, lack of native ECMAScript Module support, and inefficient implementations. By removing unnecessary logic and relying on modern browser APIs, es-toolkit achieved 2–10× performance improvements and, in some cases, reduced bundle sizes by more than 30×. Its open-source momentum attracted global contributors, eventually helping it become widely adopted. ## The Beginning of es-toolkit - Toss developers needed dependable utilities such as `throttle`, `debounce`, and `uniq`. - Although lodash was widely used, it had several limitations: - Outdated code structure and implementations. - Defensive logic for legacy browsers such as Internet Explorer. - Little use of native APIs like `Array#map`. - No ECMAScript Modules, making tree-shaking difficult. - `lodash-es` added ESM support but retained much of lodash’s older and inefficient implementation. - Toss’s internal `@toss/utils` library required significant effort to maintain and handle edge cases. - es-toolkit was created to provide a modern, efficient utility library for current web development. - Initial results showed: - At least 2× and sometimes over 10× faster execution. - Bundle-size reductions of more than 30× in some cases. ## Open-Source Adoption and Community Growth - Toss initially announced es-toolkit through its frontend social media channels. - Developers contributed missing functions, bug fixes, and performance improvements. - After gaining attention in Korea, the project was shared on Reddit and received over 100 upvotes and tens of thousands of repository visitors. - International discussions led to coverage in blogs and newsletters. - Community members created bundler plugins and migrated dependencies in established libraries from lodash to es-toolkit. ## From Contributor to Toss Developer - Dayong Lee discovered es-toolkit through Toss’s announcement and began contributing despite not being a Toss employee. - Starting with small pull requests, he gradually became the project’s second-largest contributor. - Code reviews helped him develop stronger skills in: - JavaScript language features. - API and interface design. - Open-source collaboration. - His involvement with es-toolkit eventually contributed to his joining Toss Bank. ## Making Migration Easier with `es-toolkit/compat` - Although the library was becoming more complete, adoption remained slow because many projects depended heavily on older utility libraries. - Migrating individual lodash functions across a large codebase would be tedious and risky. - es-toolkit therefore introduced `es-toolkit/compat`, a drop-in replacement designed to preserve lodash’s interfaces and behavior while modernizing its internal implementation. - This compatibility layer reduced migration effort and allowed projects to gain performance improvements by changing imports rather than rewriting utility usage. - The layer was particularly important because es-toolkit’s streamlined behavior could otherwise differ from lodash in edge cases and cause runtime errors. es-toolkit’s story demonstrates how a focused modernization effort can replace entrenched legacy dependencies. Providing both a faster native-style library and a compatibility layer made adoption more practical while enabling broad open-source participation.