Import maps for cleaner imports in Deno - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the module using the import map alias.

Deno

import { serve } from "[1]";

Drag options to blanks, or click blank then click option'

A"@std/http/server.ts"

B"std/http/server.ts"

C"http/server"

D"https://deno.land/std/http/server.ts"

Attempts:

3 left

💡 Hint

Common Mistakes

Using the full URL instead of the alias.

Using a relative path without the alias.

The import map allows using the alias @std/http/server.ts instead of the full URL.

2fill in blank

medium

Complete the import map JSON to map the alias '@utils/' to the correct URL.

Deno

{
  "imports": {
    "@utils/": "[1]"
  }
}

Drag options to blanks, or click blank then click option'

A"https://deno.land/x/utils/"

B"./utils/"

C"https://deno.land/x/std/utils/"

D"https://deno.land/std/utils/"

Attempts:

3 left

💡 Hint

Common Mistakes

Using a local relative path instead of a URL.

Using an incorrect or non-existent URL.

The alias '@utils/' maps to the standard utils URL https://deno.land/std/utils/.

3fill in blank

hard

Fix the error in the import statement to use the import map alias correctly.

Deno

import { parse } from "[1]";

Drag options to blanks, or click blank then click option'

A"std/flags/mod.ts"

B"@std/flags/mod.ts"

C"https://deno.land/std/flags/mod.ts"

D"flags/mod.ts"

Attempts:

3 left

💡 Hint

Common Mistakes

Using the full URL instead of the alias.

Using a relative path without the alias.

The import map alias @std/flags/mod.ts should be used for cleaner imports.

4fill in blank

hard

Fill both blanks to create an import map that maps '@lib/' to a local folder and '@std/' to the Deno standard library.

Deno

{
  "imports": {
    "@lib/": "[1]",
    "@std/": "[2]"
  }
}

Drag options to blanks, or click blank then click option'

A"./lib/"

B"https://deno.land/std/"

C"./src/lib/"

D"https://deno.land/x/std/"

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect URLs for the standard library.

Using absolute URLs for local folders.

The alias '@lib/' points to the local folder ./lib/, and '@std/' points to the official Deno standard library URL.

5fill in blank

hard

Fill all three blanks to create a dictionary comprehension that uses import map aliases and filters keys starting with 'a'.

Deno

const filtered = Object.fromEntries(
  Object.entries([1]).filter(([key]) => key[2]('a') [3] true)
);

Drag options to blanks, or click blank then click option'

AimportMap

B.startsWith

C!==

D===

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect string methods.

Using loose equality instead of strict equality.

This code filters entries from importMap where keys start with 'a' using .startsWith and strict equality ===.

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