Module Metadata

Concepts

• import.meta can provide information on the context of the module.
• The boolean import.meta.main will let you know if the current module is the program entry point.
• The string import.meta.url will give you the URL of the current module.
• The import.meta.resolve allows you to resolve specifier relative to the current module. This function takes into account an import map (if one was provided on startup).
• The string Deno.mainModule will give you the URL of the main module entry point, i.e. the module invoked by the deno runtime.

Example

The example below uses two modules to show the difference between import.meta.url, import.meta.main and Deno.mainModule. In this example, module_a.ts is the main module entry point:

module_b.ts

export function outputB() {
  console.log("Module B's import.meta.url", import.meta.url);
  console.log("Module B's mainModule url", Deno.mainModule);
  console.log(
    "Is module B the main module via import.meta.main?",
    import.meta.main,
  );
}

module_a.ts

import { outputB } from "./module_b.ts";

function outputA() {
  console.log("Module A's import.meta.url", import.meta.url);
  console.log("Module A's mainModule url", Deno.mainModule);
  console.log(
    "Is module A the main module via import.meta.main?",
    import.meta.main,
  );
  console.log(
    "Resolved specifier for ./module_b.ts",
    import.meta.resolve("./module_b.ts"),
  );
}

outputA();
console.log("");
outputB();

If module_a.ts is located in /home/alice/deno then the output of deno run --allow-read module_a.ts is:

Module A's import.meta.url file:///home/alice/deno/module_a.ts
Module A's mainModule url file:///home/alice/deno/module_a.ts
Is module A the main module via import.meta.main? true
Resolved specifier for ./module_b.ts file:///home/alice/deno/module_b.ts

Module B's import.meta.url file:///home/alice/deno/module_b.ts
Module B's mainModule url file:///home/alice/deno/module_a.ts
Is module B the main module via import.meta.main? false