Installing packages (dependencies vs devDependencies) in Node.js - Performance Optimization Steps

Performance: Installing packages (dependencies vs devDependencies)

MEDIUM IMPACT

This concept affects the bundle size and load time of your application by controlling which packages are included in production builds.

Managing packages for production and development environments

Node.js

npm install --save react react-dom

Runtime packages are included in production bundles, ensuring all necessary code loads correctly and quickly.

📈 Performance GainImproves LCP by avoiding runtime errors and missing code; ensures smooth page load.

Managing packages for production and development environments

Node.js

npm install --save-dev react react-dom

Installing runtime packages as devDependencies causes them to be excluded from production bundles, leading to runtime errors or missing code.

📉 Performance CostBlocks rendering due to missing runtime code; may cause failed page load or errors.

Performance Comparison

Pattern	Bundle Size Impact	Load Time Impact	Runtime Errors	Verdict
Installing runtime packages as devDependencies	Excluded from bundle	Causes runtime errors or missing code	Yes	[X] Bad
Installing runtime packages as dependencies	Included in bundle	Loads correctly and fast	No	[OK] Good
Installing build/test tools as dependencies	Increases bundle by 100-300kb+	Slows load and parse time	No	[X] Bad
Installing build/test tools as devDependencies	Excluded from production bundle	No impact on load time	No	[OK] Good

Rendering Pipeline

Package installation affects the size and content of the JavaScript bundle sent to the browser. Larger bundles increase download and parse time, delaying style calculation and paint.

→Network

→Parse & Compile

→Style Calculation

→Layout

→Paint

⚠️ BottleneckNetwork and Parse & Compile stages due to larger bundle size

Core Web Vital Affected

LCP

This concept affects the bundle size and load time of your application by controlling which packages are included in production builds.

Optimization Tips

1Always install runtime libraries as dependencies to include them in production bundles.

2Install build and test tools as devDependencies to keep production bundles small.

3Check your bundle size regularly to avoid performance regressions.

Performance Quiz - 3 Questions

Which type of package should be installed as a dependency to ensure it is included in the production bundle?

A Testing libraries like jest

B Build tools like webpack

C Runtime libraries used in the app

D Documentation tools

DevTools: Network and Performance panels

How to check: Open DevTools, go to Network panel, filter by JS files to check bundle size. Use Performance panel to record page load and see script parsing time.

What to look for: Look for large JS files increasing load time and long scripting times that delay rendering.

Practice

1. Which command installs a package as a regular dependency needed to run your Node.js app?

easy

A. npm uninstall express

B. npm install --save-dev express

C. npm install express

D. npm update express

Solution

1. Step 1: Understand the difference between dependencies and devDependencies

   Dependencies are packages needed when your app runs, while devDependencies are only needed during development.

2. Step 2: Identify the correct npm command for dependencies

   The command npm install express installs the package as a regular dependency by default.

3. Final Answer:

   npm install express -> Option C

4. Quick Check:

   Regular dependencies use npm install without flags [OK]

Hint: Use plain npm install for runtime dependencies [OK]

Common Mistakes:

• Using --save-dev for packages needed at runtime
• Confusing uninstall with install commands
• Assuming npm update installs packages

2. Which of the following commands correctly installs a package as a development dependency?

easy

A. npm install lodash

B. npm install --save-dev jest

C. npm install --prod jest

D. npm install --global jest

Solution

1. Step 1: Recognize the flag for devDependencies

   The flag --save-dev tells npm to install the package as a development dependency.

2. Step 2: Match the command with the correct flag

   npm install --save-dev jest installs Jest as a devDependency, which is used for testing during development.

3. Final Answer:

   npm install --save-dev jest -> Option B

4. Quick Check:

   Dev dependencies use --save-dev flag [OK]

Hint: Use --save-dev flag for development-only packages [OK]

Common Mistakes:

• Omitting --save-dev for dev dependencies
• Using --prod which is not a valid flag for devDependencies
• Installing globally instead of locally

3. Given the following package.json snippet, which package will NOT be installed when running npm install --production?

{
  "dependencies": {
    "express": "^4.18.2"
  },
  "devDependencies": {
    "mocha": "^10.2.0"
  }
}

medium

A. mocha

B. express

C. both express and mocha

D. neither express nor mocha

Solution

1. Step 1: Understand the effect of --production flag

   The --production flag tells npm to install only the packages listed under dependencies, skipping devDependencies.

2. Step 2: Identify which packages are devDependencies

   Here, mocha is under devDependencies, so it will NOT be installed with npm install --production.

3. Final Answer:

   mocha -> Option A

4. Quick Check:

   DevDependencies skipped with --production flag [OK]

Hint: npm install --production skips devDependencies [OK]

Common Mistakes:

• Assuming all packages install regardless of flags
• Confusing dependencies with devDependencies
• Thinking --production installs devDependencies

4. You run npm install --save-dev eslint but later realize you need eslint as a regular dependency. What is the best way to fix this?

medium

A. Run npm install eslint to add it as a dependency

B. Run npm install --save-prod eslint

C. Manually edit package.json to move eslint from devDependencies to dependencies

D. Run npm uninstall eslint then npm install eslint

Solution

1. Step 1: Understand npm behavior with existing packages

   Running npm install eslint alone will not move it from devDependencies to dependencies if already installed as devDependency.

2. Step 2: Properly remove and reinstall as dependency

   Uninstalling first removes it from devDependencies, then reinstalling adds it to dependencies.

3. Final Answer:

   Run npm uninstall eslint then npm install eslint -> Option D

4. Quick Check:

   Uninstall then install moves package between dependency types [OK]

Hint: Uninstall then reinstall to change dependency type [OK]

Common Mistakes:

• Trying to install without uninstalling first
• Editing package.json manually without reinstalling
• Using non-existent --save-prod flag

5. You want to install webpack and babel packages. webpack is needed to run your app, but babel is only needed during development. Which commands correctly install them with proper dependency types?

hard

A. npm install webpack && npm install --save-dev babel

B. npm install webpack && npm install babel

C. npm install --save-dev webpack && npm install babel

D. npm install --save-dev webpack babel

Solution

1. Step 1: Identify runtime vs development packages

   Webpack is needed at runtime, so it should be a regular dependency. Babel is only for development, so it should be a devDependency.

2. Step 2: Use correct npm commands for each

   Use npm install webpack for runtime dependency and npm install --save-dev babel for development dependency.

3. Final Answer:

   npm install webpack && npm install --save-dev babel -> Option A

4. Quick Check:

   Runtime = npm install, Dev = npm install --save-dev [OK]

Hint: Install runtime normally, dev tools with --save-dev [OK]

Common Mistakes:

• Installing all packages as devDependencies
• Installing dev tools as regular dependencies
• Using --save-dev for runtime packages