npm and package.json

npm is Node's package manager. A package.json file describes your project and its dependencies. This lesson shows how a package.json is read; the commands are what you run in a terminal.

ExampleNode.js

const pkg = JSON.parse(`{
  "name": "my-app",
  "version": "1.0.0",
  "scripts": { "start": "node index.js", "test": "node --test" },
  "dependencies": { "express": "^4.19.0" }
}`);

console.log(pkg.name, pkg.version);
console.log(Object.keys(pkg.scripts));
for (const [name, range] of Object.entries(pkg.dependencies)) {
  console.log(name, "needs", range);
}

Output

my-app 1.0.0
[ 'start', 'test' ]
express needs ^4.19.0

Useful commands: npm init -y creates a package.json, npm install express adds a package, npm run start runs a script, and npx runs a package without installing it. Packages are stored in the node_modules folder, which you never commit.

Quick check

Which file lists your project's dependencies?

package.jsonnode_modulesindex.js

Finish the quick check (and any code exercise) to complete this lesson, or mark it done yourself.

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