Node.js modules can be imported either directly by specifying a file or folder, or indirectly by specifying a module name, which will be looked up in a node_modules folder. In the latter case, care should be taken that the imported module is either bundled with the code that uses it, or declared as a dependency in the package.json file to ensure that the import does not fail at runtime.

Declare the dependency in the package.json file or include an externs file for it during extraction.

Externs files for all the core packages of Node.js are available in the tool/data/externs/nodejs directory of the distribution, and are included by default for projects created using bootstrap.

In the following example, the package.json file specifies no dependencies, but index.js imports acorn. This import will fail unless a copy of acorn happens to be installed (for instance in the user's node_modules folder). On the other hand, the import of fs is unproblematic, since fs is a standard module that is included with every Node.js installation.

The dependency on acorn should be declared in the package.json file:

Node.js Manual: Module resolution algorithm.