Import maps for cleaner imports in Deno - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is an import map in Deno?

An import map is a JSON file that lets you define custom paths or aliases for module imports. It helps make import statements cleaner and easier to manage.

beginner

How do import maps improve code readability?

Import maps let you replace long URLs or paths with short, meaningful names. This makes the code easier to read and maintain, like using nicknames instead of full names.

beginner

How do you tell Deno to use an import map file?

You run your Deno program with the flag --import-map=path/to/import_map.json. This tells Deno to apply the import map when resolving imports.

intermediate

Example snippet of an import map JSON file?

{
  "imports": {
    "lodash": "https://cdn.skypack.dev/lodash"
  }
}
This maps the name 'lodash' to the full URL, so you can import 'lodash' directly.

intermediate

What happens if an import is not found in the import map?

Deno tries to resolve the import as usual, using the path or URL given in the import statement. The import map only changes imports it knows about.

What is the main purpose of an import map in Deno?

A To manage environment variables

B To compile TypeScript to JavaScript

C To create shortcuts for module imports

D To run Deno scripts faster

Import maps let you create shortcuts or aliases for module imports, making code cleaner.

How do you apply an import map when running a Deno script?

A Set an environment variable

B Use --import-map flag with the file path

C Add import map inside the script file

D Use a special import statement

You use the --import-map flag followed by the path to the import map JSON file.

If an import is not listed in the import map, what does Deno do?

A Throws an error immediately

B Uses a default import map

C Ignores the import

D Resolves the import normally using the given path or URL

Deno resolves imports normally if they are not found in the import map.

Which file format is used for import maps?

A JSON

B YAML

C XML

D Plain text

Import maps are defined using JSON format.

What is a benefit of using import maps for imports?

A They allow using shorter, meaningful import names

B They speed up network requests

C They encrypt your code

D They automatically update dependencies

Import maps let you use shorter and clearer names instead of long URLs or paths.

Explain what an import map is and how it helps in Deno projects.

Think about how you can replace long URLs with short names.

Describe the steps to create and use an import map in a Deno project.

Consider the JSON structure and the command line flag.

Practice

1. What is the main purpose of using import maps in Deno?

easy

A. To automatically update all dependencies to their latest versions

B. To speed up the execution of Deno scripts

C. To compile TypeScript files into JavaScript

D. To replace long URLs with short, easy-to-read names in imports

Solution

1. Step 1: Understand what import maps do

   Import maps allow you to map long URLs to short names, making imports cleaner.

2. Step 2: Identify the main benefit

   This makes code easier to read and maintain by avoiding long URLs in import statements.

3. Final Answer:

   To replace long URLs with short, easy-to-read names in imports -> Option D

4. Quick Check:

   Import maps = cleaner imports [OK]

Hint: Import maps shorten URLs to simple names [OK]

Common Mistakes:

• Thinking import maps speed up code execution
• Confusing import maps with dependency updates
• Believing import maps compile code

2. Which command correctly runs a Deno script using an import map file named imports.json?

easy

A. deno run --importmap imports.json script.ts

B. deno run --import-map=imports.json script.ts

C. deno run --map-import=imports.json script.ts

D. deno run -importmap imports.json script.ts

Solution

1. Step 1: Recall the correct flag syntax

   The correct flag to specify an import map file is --import-map=.

2. Step 2: Match the command with correct syntax

   deno run --import-map=imports.json script.ts uses --import-map=imports.json, which is the correct form.

3. Final Answer:

   deno run --import-map=imports.json script.ts -> Option B

4. Quick Check:

   Use --import-map=filename [OK]

Hint: Use double dash and equal sign for import map flag [OK]

Common Mistakes:

• Using single dash instead of double dash
• Missing equal sign between flag and filename
• Using incorrect flag names like --map-import

3. Given this imports.json file:

{
  "imports": {
    "lodash": "https://cdn.skypack.dev/lodash"
  }
}

And this code:

import _ from "lodash";
console.log(typeof _);

What will be printed when running with --import-map=imports.json?

medium

A. "object"

B. "undefined"

C. SyntaxError

D. "function"

Solution

1. Step 1: Understand import map effect

   The import map maps "lodash" to the URL, so the import fetches lodash library.

2. Step 2: Check lodash type

   Lodash is an object with many functions, so typeof _ returns "object".

3. Final Answer:

   "object" -> Option A

4. Quick Check:

   Import maps load modules correctly = "object" [OK]

Hint: Mapped imports load modules, typeof lodash is object [OK]

Common Mistakes:

• Expecting 'undefined' because of missing URL
• Thinking import maps cause syntax errors
• Assuming lodash is a function type

4. You wrote this import map file imports.json:

{
  "imports": {
    "react": "https://cdn.skypack.dev/react"
  }
}

But running deno run --import-map=imports.json app.ts gives an error: Cannot resolve module "react". What is the likely cause?

medium

A. The import map file is not valid JSON

B. The import map file is not passed correctly to the command

C. The import statement in app.ts uses a different name than "react"

D. Deno does not support import maps

Solution

1. Step 1: Check import map correctness

   The JSON looks valid and the flag is used correctly, so those are unlikely causes.

2. Step 2: Check import statement in app.ts

   If the import statement uses a different name than "react", Deno won't find it in the map and errors.

3. Final Answer:

   The import statement in app.ts uses a different name than "react" -> Option C

4. Quick Check:

   Import name must match map key [OK]

Hint: Import name must exactly match import map key [OK]

Common Mistakes:

• Assuming import map file is invalid without checking
• Forgetting to pass import map flag
• Believing Deno lacks import map support

5. You want to use two libraries, lodash and dayjs, with import maps to keep your code clean. Your imports.json is:

{
  "imports": {
    "lodash": "https://cdn.skypack.dev/lodash",
    "dayjs": "https://cdn.skypack.dev/dayjs"
  }
}

In your code, you write:

import _ from "lodash";
import dayjs from "dayjs";
console.log(dayjs().format());

What must you do to run this code correctly in Deno?

hard

A. Run with deno run --import-map=imports.json script.ts and ensure internet access

B. Run with deno run script.ts only, import maps are automatic

C. Include both libraries locally and import from relative paths

D. Use --allow-net flag without import maps

Solution

1. Step 1: Recognize import map usage

   To use import maps, you must run Deno with the --import-map flag pointing to your map file.

2. Step 2: Understand network requirement

   Since the URLs are remote, Deno needs internet access to fetch them, so network permission is needed.

3. Final Answer:

   Run with deno run --import-map=imports.json script.ts and ensure internet access -> Option A

4. Quick Check:

   Use --import-map and allow network [OK]

Hint: Always use --import-map flag and allow network for remote URLs [OK]

Common Mistakes:

• Running without --import-map flag
• Assuming import maps work automatically
• Not allowing network access for remote imports