The Hidden Cost of String Interning in Modern Bundlers
String interning is a common optimization in modern JavaScript bundlers like Webpack, Rollup, and esbuild, but it carries hidden costs that can degrade performance, increase memory usage, and complicate debugging. This article delves deep into the mechanics of string interning, revealing how bundlers deduplicate strings at build time and the trade-offs that arise in large-scale applications. We explore real-world scenarios where interning leads to inflated bundle sizes, slower build times, and runtime overhead. Through detailed comparisons of bundler internals, step-by-step debugging guides, and practical mitigation strategies, experienced developers will learn how to identify and prevent interning pitfalls. Topics include memory fragmentation in module graphs, conflicts with code splitting, and interactions with tree shaking. The article also covers tooling considerations, such as configuring custom string pools and using AST analysis to audit interning behavior. A comprehensive FAQ addresses common questions about interning in monorepos, incremental builds, and legacy codebases. By the end, readers will have actionable techniques to optimize their bundling pipeline without sacrificing readability or maintainability. This guide is designed for senior engineers and performance architects who need to understand the true cost of seemingly innocent optimizations.