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NPM scripts memo

There is an extremely brief but too informative summary about such convenient feature of npm as scripts. So few words, only grouped and classified facts.

Disclamer

Information is relevant for npm v9.2.0

Main purposes of this post

  • to introduce classification of scripts
  • to summarize important things about npm scripts
  • to act as a quick reminder about npm scripts

Prerequisites

The readers should already be familiar with npm scripts feature at least at elementary level. It can be learned from scratch using some other sources:


Classification

  1. Natively supported scripts
  2. Arbitrary scripts

1 Natively supported

Purpose

To include developer-defined actions into npm command's flow (e.g., npm pack, npm install)

Where defined

package.json, "scripts" object

When executed

As a part of certain npm command - before or after the main action that performed by this command

How to run

npm <command-name>


Native scripts can be classified into Lifecycle, Action-specific, Command-specific scripts.


1-1 Lifecycle scripts

Description

Wide specific scripts. Run in the flow of several npm commands.

Scripts

  • preprepare/prepare/postprepare
  • dependencies

Example

prepare script is run in the flow of...

...next commands:
  • npm cache add
  • npm ci
  • npm diff
  • npm install
  • npm pack
  • npm publish
  • npm rebuild

See more here.


1-2 Action-specific scripts

Description

Run in the flow of one npm command along with command's main action. Some scripts run in more than one commands those perform related actions.

Scripts

  • prepublish - in flow of npm ci, npm install
  • prepublishOnly - in flow of npm publish
  • prepack/postpack - in flow of npm pack, npm publish
  • preinstall/install/postinstall - in flow of npm ci, npm install, npm rebuild
  • preversion/version/postversion - in flow of npm version

Example

npm version commands run the flow that includes its main action and predefined scripts. Execution order:

  • preversion script
  • npm version command's action
  • version script
  • postversion script

See more here.


1-3 Command-specific scripts

Description

Run in response of exactly one built-in npm command. These commands don't have their own actions and only run predefined scripts

Scripts

  • prestart/start/poststart - in response of npm start
  • prerestart/restart/postrestart - in response of npm restart
  • prestop/stop/poststop - in response of npm stop
  • pretest/test/posttest - in response of npm test

Example

npm start performs the next operations in order:

  • prestart script
  • start script
  • poststart script

This command doesn't have its own action other than scripts running.


2 Arbitrary

Purpose

To perform developer-defined tasks using npm ecosystem

Motivation

There may be other ways to perform developer-defined tasks, but it's handy to use npm ecosystem for them

How to define:

package.json, "scripts" object

When executed

In response of npm run command that runs exactly certain script named script-name

How to run

npm run[-script] <script-name>

Important

Arbitrary scripts can have pre/post versions

Example

Given we have precompress, compress and postcompress scripts in package.json.

npm run[-script] compress performs the next:

  • precompress script
  • compress script
  • postcompress script

So arbitrary scripts are similar to Command-specific native scripts. But they don't have a specific built-in npm command for running them.


This was a brief summary about npm scripts. I'm glad to receive a feedback!

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