Import Maps

In order for Deno to resolve a bare specifier like "react" or "lodash", it needs to be told where to look for it. Does "lodash" refer to an module in our project or does it refer to a third party dependency? Deno needs to know where to resolve the import specifier lodash to.

import lodash from "lodash";

We can point Deno to the lodash package on npm, for example, by adding it to the "imports" section in deno.json.

{
  "imports": {
    "lodash": "npm:lodash@^4.17"
  }
}

The "imports" section in deno.json is often referred to as an import map that is based on the Import Maps Standard.

You may have seen Node and npm use package.json and the node_modules folder to do similar package resolution.

The deno.json file is auto-discovered and acts (among other things) as an import map. Read more about deno.json here.

Using third party modules is explained further in ECMAScript Modules.

Custom path mappings Jump to heading#

The import map in deno.json can be used for more general path mapping of specifiers. You can map an exact specifiers to a third party module or a file directly, or you can map a part of an import specifier to a directory.

{
  "imports": {
    // Map to an exact file
    "foo": "./some/long/path/foo.ts",
    // Map to a directory, usage: "bar/file.ts"
    "bar/": "./some/folder/bar/"
  }
}

Usage:

import * as foo from "foo";
import * as bar from "bar/file.ts";

Path mapping of import specifies is commonly used in larger code bases for brevity.

To use your project root for absolute imports:

{
  "imports": {
    "/": "./",
    "./": "./"
  }
}

import { MyUtil } from "/util.ts";

This causes import specifiers starting with / to be resolved relative to the import map's URL or file path.