1---
2title: scripts
3section: 7
4description: How npm handles the "scripts" field
5---
6
7### Description
8
9The `"scripts"` property of your `package.json` file supports a number
10of built-in scripts and their preset life cycle events as well as
11arbitrary scripts. These all can be executed by running
12`npm run-script <stage>` or `npm run <stage>` for short. *Pre* and *post*
13commands with matching names will be run for those as well (e.g. `premyscript`,
14`myscript`, `postmyscript`). Scripts from dependencies can be run with
15`npm explore <pkg> -- npm run <stage>`.
16
17### Pre & Post Scripts
18
19To create "pre" or "post" scripts for any scripts defined in the
20`"scripts"` section of the `package.json`, simply create another script
21*with a matching name* and add "pre" or "post" to the beginning of them.
22
23```json
24{
25  "scripts": {
26    "precompress": "{{ executes BEFORE the `compress` script }}",
27    "compress": "{{ run command to compress files }}",
28    "postcompress": "{{ executes AFTER `compress` script }}"
29  }
30}
31```
32
33In this example `npm run compress` would execute these scripts as
34described.
35
36### Life Cycle Scripts
37
38There are some special life cycle scripts that happen only in certain
39situations. These scripts happen in addition to the `pre<event>`, `post<event>`, and
40`<event>` scripts.
41
42* `prepare`, `prepublish`, `prepublishOnly`, `prepack`, `postpack`, `dependencies`
43
44**prepare** (since `npm@4.0.0`)
45* Runs BEFORE the package is packed, i.e. during `npm publish`
46    and `npm pack`
47* Runs on local `npm install` without any arguments
48* Runs AFTER `prepublish`, but BEFORE `prepublishOnly`
49
50* NOTE: If a package being installed through git contains a `prepare`
51 script, its `dependencies` and `devDependencies` will be installed, and
52 the prepare script will be run, before the package is packaged and
53 installed.
54
55* As of `npm@7` these scripts run in the background.
56  To see the output, run with: `--foreground-scripts`.
57
58**prepublish** (DEPRECATED)
59* Does not run during `npm publish`, but does run during `npm ci`
60  and `npm install`. See below for more info.
61
62**prepublishOnly**
63* Runs BEFORE the package is prepared and packed, ONLY on `npm publish`.
64
65**prepack**
66* Runs BEFORE a tarball is packed (on "`npm pack`", "`npm publish`", and when installing a git dependency).
67* NOTE: "`npm run pack`" is NOT the same as "`npm pack`". "`npm run pack`" is an arbitrary user defined script name, where as, "`npm pack`" is a CLI defined command.
68
69**postpack**
70* Runs AFTER the tarball has been generated but before it is moved to its final destination (if at all, publish does not save the tarball locally)
71
72**dependencies**
73* Runs AFTER any operations that modify the `node_modules` directory IF changes occurred.
74* Does NOT run in global mode
75
76#### Prepare and Prepublish
77
78**Deprecation Note: prepublish**
79
80Since `npm@1.1.71`, the npm CLI has run the `prepublish` script for both `npm publish` and `npm install`, because it's a convenient way to prepare a package for use (some common use cases are described in the section below).  It has also turned out to be, in practice, [very confusing](https://github.com/npm/npm/issues/10074).  As of `npm@4.0.0`, a new event has been introduced, `prepare`, that preserves this existing behavior. A _new_ event, `prepublishOnly` has been added as a transitional strategy to allow users to avoid the confusing behavior of existing npm versions and only run on `npm publish` (for instance, running the tests one last time to ensure they're in good shape).
81
82See <https://github.com/npm/npm/issues/10074> for a much lengthier justification, with further reading, for this change.
83
84**Use Cases**
85
86If you need to perform operations on your package before it is used, in a way that is not dependent on the operating system or architecture of the target system, use a `prepublish` script. This includes tasks such as:
87
88* Compiling CoffeeScript source code into JavaScript.
89* Creating minified versions of JavaScript source code.
90* Fetching remote resources that your package will use.
91
92The advantage of doing these things at `prepublish` time is that they can be done once, in a single place, thus reducing complexity and variability. Additionally, this means that:
93
94* You can depend on `coffee-script` as a `devDependency`, and thus
95  your users don't need to have it installed.
96* You don't need to include minifiers in your package, reducing
97  the size for your users.
98* You don't need to rely on your users having `curl` or `wget` or
99  other system tools on the target machines.
100
101#### Dependencies
102
103The `dependencies` script is run any time an `npm` command causes changes to the `node_modules` directory. It is run AFTER the changes have been applied and the `package.json` and `package-lock.json` files have been updated.
104
105### Life Cycle Operation Order
106
107#### [`npm cache add`](/commands/npm-cache)
108
109* `prepare`
110
111#### [`npm ci`](/commands/npm-ci)
112
113* `preinstall`
114* `install`
115* `postinstall`
116* `prepublish`
117* `preprepare`
118* `prepare`
119* `postprepare`
120
121 These all run after the actual installation of modules into
122 `node_modules`, in order, with no internal actions happening in between
123
124#### [`npm diff`](/commands/npm-diff)
125
126* `prepare`
127
128#### [`npm install`](/commands/npm-install)
129
130These also run when you run `npm install -g <pkg-name>`
131
132* `preinstall`
133* `install`
134* `postinstall`
135* `prepublish`
136* `preprepare`
137* `prepare`
138* `postprepare`
139
140If there is a `binding.gyp` file in the root of your package and you
141haven't defined your own `install` or `preinstall` scripts, npm will
142default the `install` command to compile using node-gyp via `node-gyp
143rebuild`
144
145These are run from the scripts of `<pkg-name>`
146
147#### [`npm pack`](/commands/npm-pack)
148
149* `prepack`
150* `prepare`
151* `postpack`
152
153#### [`npm publish`](/commands/npm-publish)
154
155* `prepublishOnly`
156* `prepack`
157* `prepare`
158* `postpack`
159* `publish`
160* `postpublish`
161
162#### [`npm rebuild`](/commands/npm-rebuild)
163
164* `preinstall`
165* `install`
166* `postinstall`
167* `prepare`
168
169`prepare` is only run if the current directory is a symlink (e.g. with
170linked packages)
171
172#### [`npm restart`](/commands/npm-restart)
173
174If there is a `restart` script defined, these events are run, otherwise
175`stop` and `start` are both run if present, including their `pre` and
176`post` iterations)
177
178* `prerestart`
179* `restart`
180* `postrestart`
181
182#### [`npm run <user defined>`](/commands/npm-run-script)
183
184* `pre<user-defined>`
185* `<user-defined>`
186* `post<user-defined>`
187
188#### [`npm start`](/commands/npm-start)
189
190* `prestart`
191* `start`
192* `poststart`
193
194If there is a `server.js` file in the root of your package, then npm
195will default the `start` command to `node server.js`.  `prestart` and
196`poststart` will still run in this case.
197
198#### [`npm stop`](/commands/npm-stop)
199
200* `prestop`
201* `stop`
202* `poststop`
203
204#### [`npm test`](/commands/npm-test)
205
206* `pretest`
207* `test`
208* `posttest`
209
210#### [`npm version`](/commands/npm-version)
211
212* `preversion`
213* `version`
214* `postversion`
215
216#### A Note on a lack of [`npm uninstall`](/commands/npm-uninstall) scripts
217
218While npm v6 had `uninstall` lifecycle scripts, npm v7 does not. Removal of a package can happen for a wide variety of reasons, and there's no clear way to currently give the script enough context to be useful.
219
220Reasons for a package removal include:
221
222* a user directly uninstalled this package
223* a user uninstalled a dependant package and so this dependency is being uninstalled
224* a user uninstalled a dependant package but another package also depends on this version
225* this version has been merged as a duplicate with another version
226* etc.
227
228Due to the lack of necessary context, `uninstall` lifecycle scripts are not implemented and will not function.
229
230### User
231
232When npm is run as root, scripts are always run with the effective uid
233and gid of the working directory owner.
234
235### Environment
236
237Package scripts run in an environment where many pieces of information
238are made available regarding the setup of npm and the current state of
239the process.
240
241#### path
242
243If you depend on modules that define executable scripts, like test
244suites, then those executables will be added to the `PATH` for
245executing the scripts.  So, if your package.json has this:
246
247```json
248{
249  "name" : "foo",
250  "dependencies" : {
251    "bar" : "0.1.x"
252  },
253  "scripts": {
254    "start" : "bar ./test"
255  }
256}
257```
258
259then you could run `npm start` to execute the `bar` script, which is
260exported into the `node_modules/.bin` directory on `npm install`.
261
262#### package.json vars
263
264The package.json fields are tacked onto the `npm_package_` prefix. So,
265for instance, if you had `{"name":"foo", "version":"1.2.5"}` in your
266package.json file, then your package scripts would have the
267`npm_package_name` environment variable set to "foo", and the
268`npm_package_version` set to "1.2.5".  You can access these variables
269in your code with `process.env.npm_package_name` and
270`process.env.npm_package_version`, and so on for other fields.
271
272See [`package.json`](/configuring-npm/package-json) for more on package configs.
273
274#### current lifecycle event
275
276Lastly, the `npm_lifecycle_event` environment variable is set to
277whichever stage of the cycle is being executed. So, you could have a
278single script used for different parts of the process which switches
279based on what's currently happening.
280
281Objects are flattened following this format, so if you had
282`{"scripts":{"install":"foo.js"}}` in your package.json, then you'd
283see this in the script:
284
285```bash
286process.env.npm_package_scripts_install === "foo.js"
287```
288
289### Examples
290
291For example, if your package.json contains this:
292
293```json
294{
295  "scripts" : {
296    "install" : "scripts/install.js",
297    "postinstall" : "scripts/install.js"
298  }
299}
300```
301
302then `scripts/install.js` will be called for the install and post-install
303stages of the lifecycle.  Since `scripts/install.js` is running for two
304different phases, it would be wise in this case to look at the
305`npm_lifecycle_event` environment variable.
306
307If you want to run a make command, you can do so.  This works just
308fine:
309
310```json
311{
312  "scripts" : {
313    "preinstall" : "./configure",
314    "install" : "make && make install",
315    "test" : "make test"
316  }
317}
318```
319
320### Exiting
321
322Scripts are run by passing the line as a script argument to `sh`.
323
324If the script exits with a code other than 0, then this will abort the
325process.
326
327Note that these script files don't have to be Node.js or even
328JavaScript programs. They just have to be some kind of executable
329file.
330
331### Best Practices
332
333* Don't exit with a non-zero error code unless you *really* mean it.
334  If the failure is minor or only will prevent some optional features, then
335  it's better to just print a warning and exit successfully.
336* Try not to use scripts to do what npm can do for you.  Read through
337  [`package.json`](/configuring-npm/package-json) to see all the things that you can specify and enable
338  by simply describing your package appropriately.  In general, this
339  will lead to a more robust and consistent state.
340* Inspect the env to determine where to put things.  For instance, if
341  the `npm_config_binroot` environment variable is set to `/home/user/bin`, then
342  don't try to install executables into `/usr/local/bin`.  The user
343  probably set it up that way for a reason.
344* Don't prefix your script commands with "sudo".  If root permissions
345  are required for some reason, then it'll fail with that error, and
346  the user will sudo the npm command in question.
347* Don't use `install`. Use a `.gyp` file for compilation, and `prepare`
348  for anything else. You should almost never have to explicitly set a
349  preinstall or install script. If you are doing this, please consider if
350  there is another option. The only valid use of `install` or `preinstall`
351  scripts is for compilation which must be done on the target architecture.
352* Scripts are run from the root of the package folder, regardless of what the
353  current working directory is when `npm` is invoked. If you want your
354  script to use different behavior based on what subdirectory you're in, you
355  can use the `INIT_CWD` environment variable, which holds the full path you
356  were in when you ran `npm run`.
357
358### See Also
359
360* [npm run-script](/commands/npm-run-script)
361* [package.json](/configuring-npm/package-json)
362* [npm developers](/using-npm/developers)
363* [npm install](/commands/npm-install)
364