What is type: module in package.json?

Let's understand this mysterious option

Background

When trying to use 'import' statements in a Node.js project, you often encounter the error SyntaxError: Cannot use import statement outside a module. This means you cannot use import statements outside of a module, but what is a module and why can't we use import?

CommonJS and ECMA Script Modules

CJS and ESM are both module systems. The original JavaScript didn't have a module system, but when JavaScript started being used for backend development, the CommonJS module system was created and became the de facto standard.

Since CommonJS wasn't an official standard, the ECMA Script Modules module system was newly established as a standard, with different syntax and internal structure from CommonJS for utilizing modules.

As a side note, the ESM module system and ECMAScript specification versions like 'ES6, ES7, ES8' are different things.

Conclusion

The type in package.json specifies which module system the current package will use.

{
  "name": "node_jwt",
  "version": "1.0.0",
  "type": "module",
  ...
}

When specifying type: module, it means you will use the 'ESM' module system, and therefore you must use module syntax that matches ESM. When specifying type: commonjs or nothing at all, you use the CommonJS syntax with require() statements.

Since the import from statement I wanted to use is ESM syntax, I added type: module to my project.

Javascript