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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 string import.meta.filename will give you the fully resolved path to the current module. For local modules only.
  • The string import.meta.dirname will give you the fully resolved path to the directory containing the current module. For local modules only.
  • 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