1. What is package.json?
package.json is the heart of any Node.js project. It declares your project’s dependencies and provides metadata about your application.

Key Features

• Lists dependencies and devDependencies.
• Specifies version ranges using semantic versioning ( ^ , ~ ).
• Includes project metadata like name, version, scripts, author, and license.
• Human-readable and editable.

{
  "name": "my-app",
  "version": "1.0.0",
  "dependencies": {
    "lodash": "^4.17.21"
  },
  "devDependencies": {
    "jest": "~29.0.0"
  },
  "scripts": {
    "start": "node index.js"
  }
}

Key Point: package.json specifies what versions your project is compatible with , not the exact installed version.

2. What is package-lock.json?
package-lock.json is automatically generated by npm to lock the exact versions of every installed package, including nested dependencies.

Key Features

• Records the exact version installed for each package.
• Contains resolved URLs and integrity hashes to ensure packages are not tampered with.
• Records nested dependencies (dependencies of dependencies).
• Not intended for manual editing.

{
  "name": "my-app",
  "lockfileVersion": 3,
  "dependencies": {
    "lodash": {
      "version": "4.17.21",
      "resolved": "https://registry.npmjs.org/lodash/-/lodash-4.17.21.tgz",
      "integrity": "sha512-xyz"
    }
  }
}

Key Point: package-lock.json ensures that every environment installs exactly the same versions , even if package.json allows ranges.

3. Main Differences Between package.json and package-lock.json

4. How npm install Works

The npm install command is used to install packages based on package.json and package-lock.json.

# Install all dependencies listed in package.json
npm install

# Install a specific package and save it to dependencies
npm install lodash

# Install a package as a dev dependency
npm install --save-dev jest

# Install a package globally
npm install -g typescript

Process

• Reads package.json for dependencies.
• Resolves the latest versions allowed by version ranges (if package-lock.json doesn’t exist).
• Downloads packages to node_modules.
• Updates or creates package-lock.json with exact versions.

5. What Happens If You Delete package-lock.json?

If package-lock.json is deleted and you run:

npm install

• npm will resolve latest versions matching the ranges in package.json.
• Download new packages and regenerate package-lock.json.
• This may result in different versions from the previous install, which could break your code.

Safe scenarios for deleting:

• Intentionally updating packages.
• Starting a fresh project or refreshing dependencies.

Why are both files important

• package.json defines what your project needs.
• package-lock.json ensures everyone gets the exact same package versions for consistent development and production environments.

Conclusion
package.json = “What I want” (dependency ranges and project info)
package-lock.json = “Exactly what I got” (locked versions)

Deleting package-lock.json can lead to installing newer package versions, which may cause unexpected issues. Always commit package-lock.json to version control for consistency.