How Node.js Module Resolution Algorithm Finds the Right File or Package

When a Node.js application calls require(), the runtime must convert the string argument into an actual file or module before any code can execute — a process called Module Resolution. Node.js classifies every require() call into one of three categories: Core Modules bundled with the runtime, Local Modules written by the developer, and Third-Party Modules installed via npm. Core Modules such as fs, http, and path are resolved first and fastest, as Node checks for a core match immediately and skips any filesystem search if one is found. This prioritization is why require('fs') loads near-instantly without scanning directories or node_modules folders. Understanding this algorithm matters because a typical Node.js application triggers it hundreds or thousands of times during startup alone.