Module resolution

Learn moduleResolution options.

What is moduleResolution?

moduleResolution determines how an import statement finds its target file. Common values: node (classic Node resolution), node16/nodenext (Node 16+ rules), and bundler (for Vite, webpack, and similar).

{
  "compilerOptions": {
    "moduleResolution": "bundler"
  }
}

bundler allows extensionless imports; node16 requires full extensions.

node vs node16 vs bundler

node is classic CommonJS resolution and allows extensionless imports. node16/nodenext applies ESM rules and requires the .js extension. bundler mimics bundler behavior and is independent of the module option.

// node16: import "./foo.js"  // extension required
// bundler: import "./foo"    // extensionless OK

A wrong choice can cause runtime module-not-found errors.

Exercise Resolve the module path

Write a resolveModule function taking specifier and strategy. For bundler return an extensionless string, for node16 a .js extension string, and for node a classic resolution string. Print the result of resolveModule("./foo", "bundler").

Show example solution

type Resolution = "node" | "node16" | "bundler";

function resolveModule(specifier: string, strategy: Resolution): string {
  if (strategy === "bundler") {
    return specifier + " (no extension required)";
  }
  if (strategy === "node16") {
    return specifier + ".js (full path required)";
  }
  return specifier + " (node classic)";
}

console.log(resolveModule("./foo", "bundler"));

Test yourself

Which moduleResolution suits a project using Vite or webpack?
- node16
- classic
- bundler
- amd
Show answer

bundler — bundler is designed for bundler-based projects and allows extensionless imports; node16 requires full extensions, and classic and amd are not suited to modern bundlers.

Choose bundler resolution

{
  "compilerOptions": {
    "moduleResolution": "____"
  }
}

Show answer

{
  "compilerOptions": {
    "moduleResolution": "bundler"
  }
}

Resolution strategies

node

classic CommonJS resolution
node16

ESM rules, extension required
bundler

bundler behavior
nodenext

equivalent to node16

Next lesson: Path mapping

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