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1 ---
2 title: scripts
3 section: 7
4 description: How npm handles the "scripts" field
5 github_repo: npm/cli
6 github_branch: release/v9
7 github_path: docs/lib/content/using-npm/scripts.md
8 redirect_from:
9 - /cli-documentation/v9/misc/scripts
10 - /cli-documentation/v9/using-npm/scripts
11 - /cli/v9/misc/scripts
12 ---
13
14 ### Description
15
16 The `"scripts"` property of your `package.json` file supports a number of built-in scripts and their preset life cycle events as well as arbitrary scripts. These all can be executed by running `npm run-script <stage>` or `npm run <stage>` for short. _Pre_ and _post_ commands with matching names will be run for those as well (e.g. `premyscript`, `myscript`, `postmyscript`). Scripts from dependencies can be run with `npm explore <pkg> -- npm run <stage>`.
17
18 ### Pre & Post Scripts
19
20 To create "pre" or "post" scripts for any scripts defined in the `"scripts"` section of the `package.json`, simply create another script _with a matching name_ and add "pre" or "post" to the beginning of them.
21
22 ```json
23 {
24 "scripts": {
25 "precompress": "{{ executes BEFORE the `compress` script }}",
26 "compress": "{{ run command to compress files }}",
27 "postcompress": "{{ executes AFTER `compress` script }}"
28 }
29 }
30 ```
31
32 In this example `npm run compress` would execute these scripts as described.
33
34 ### Life Cycle Scripts
35
36 There are some special life cycle scripts that happen only in certain situations. These scripts happen in addition to the `pre<event>`, `post<event>`, and `<event>` scripts.
37
38 - `prepare`, `prepublish`, `prepublishOnly`, `prepack`, `postpack`, `dependencies`
39
40 **prepare** (since `npm@4.0.0`)
41
42 - Runs BEFORE the package is packed, i.e. during `npm publish` and `npm pack`
43 - Runs on local `npm install` without any arguments
44 - Runs AFTER `prepublish`, but BEFORE `prepublishOnly`
45
46 - NOTE: If a package being installed through git contains a `prepare` script, its `dependencies` and `devDependencies` will be installed, and the prepare script will be run, before the package is packaged and installed.
47
48 - As of `npm@7` these scripts run in the background. To see the output, run with: `--foreground-scripts`.
49
50 **prepublish** (DEPRECATED)
51
52 - Does not run during `npm publish`, but does run during `npm ci` and `npm install`. See below for more info.
53
54 **prepublishOnly**
55
56 - Runs BEFORE the package is prepared and packed, ONLY on `npm publish`.
57
58 **prepack**
59
60 - Runs BEFORE a tarball is packed (on "`npm pack`", "`npm publish`", and when installing a git dependency).
61 - 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.
62
63 **postpack**
64
65 - 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)
66
67 **dependencies**
68
69 - Runs AFTER any operations that modify the `node_modules` directory IF changes occurred.
70 - Does NOT run in global mode
71
72 #### Prepare and Prepublish
73
74 **Deprecation Note: prepublish**
75
76 Since `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).
77
78 See [https://github.com/npm/npm/issues/10074](https://github.com/npm/npm/issues/10074) for a much lengthier justification, with further reading, for this change.
79
80 **Use Cases**
81
82 If 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:
83
84 - Compiling CoffeeScript source code into JavaScript.
85 - Creating minified versions of JavaScript source code.
86 - Fetching remote resources that your package will use.
87
88 The 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:
89
90 - You can depend on `coffee-script` as a `devDependency`, and thus your users don't need to have it installed.
91 - You don't need to include minifiers in your package, reducing the size for your users.
92 - You don't need to rely on your users having `curl` or `wget` or other system tools on the target machines.
93
94 #### Dependencies
95
96 The `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.
97
98 ### Life Cycle Operation Order
99
100 #### [`npm cache add`](/cli/v9/commands/npm-cache)
101
102 - `prepare`
103
104 #### [`npm ci`](/cli/v9/commands/npm-ci)
105
106 - `preinstall`
107 - `install`
108 - `postinstall`
109 - `prepublish`
110 - `preprepare`
111 - `prepare`
112 - `postprepare`
113
114 These all run after the actual installation of modules into `node_modules`, in order, with no internal actions happening in between
115
116 #### [`npm diff`](/cli/v9/commands/npm-diff)
117
118 - `prepare`
119
120 #### [`npm install`](/cli/v9/commands/npm-install)
121
122 These also run when you run `npm install -g <pkg-name>`
123
124 - `preinstall`
125 - `install`
126 - `postinstall`
127 - `prepublish`
128 - `preprepare`
129 - `prepare`
130 - `postprepare`
131
132 If there is a `binding.gyp` file in the root of your package and you haven't defined your own `install` or `preinstall` scripts, npm will default the `install` command to compile using node-gyp via `node-gyp rebuild`
133
134 These are run from the scripts of `<pkg-name>`
135
136 #### [`npm pack`](/cli/v9/commands/npm-pack)
137
138 - `prepack`
139 - `prepare`
140 - `postpack`
141
142 #### [`npm publish`](/cli/v9/commands/npm-publish)
143
144 - `prepublishOnly`
145 - `prepack`
146 - `prepare`
147 - `postpack`
148 - `publish`
149 - `postpublish`
150
151 `prepare` will not run during `--dry-run`
152
153 #### [`npm rebuild`](/cli/v9/commands/npm-rebuild)
154
155 - `preinstall`
156 - `install`
157 - `postinstall`
158 - `prepare`
159
160 `prepare` is only run if the current directory is a symlink (e.g. with linked packages)
161
162 #### [`npm restart`](/cli/v9/commands/npm-restart)
163
164 If there is a `restart` script defined, these events are run, otherwise `stop` and `start` are both run if present, including their `pre` and `post` iterations)
165
166 - `prerestart`
167 - `restart`
168 - `postrestart`
169
170 #### [`npm run <user defined>`](/cli/v9/commands/npm-run-script)
171
172 - `pre<user-defined>`
173 - `<user-defined>`
174 - `post<user-defined>`
175
176 #### [`npm start`](/cli/v9/commands/npm-start)
177
178 - `prestart`
179 - `start`
180 - `poststart`
181
182 If there is a `server.js` file in the root of your package, then npm will default the `start` command to `node server.js`. `prestart` and `poststart` will still run in this case.
183
184 #### [`npm stop`](/cli/v9/commands/npm-stop)
185
186 - `prestop`
187 - `stop`
188 - `poststop`
189
190 #### [`npm test`](/cli/v9/commands/npm-test)
191
192 - `pretest`
193 - `test`
194 - `posttest`
195
196 #### [`npm version`](/cli/v9/commands/npm-version)
197
198 - `preversion`
199 - `version`
200 - `postversion`
201
202 #### A Note on a lack of [`npm uninstall`](/cli/v9/commands/npm-uninstall) scripts
203
204 While 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.
205
206 Reasons for a package removal include:
207
208 - a user directly uninstalled this package
209 - a user uninstalled a dependant package and so this dependency is being uninstalled
210 - a user uninstalled a dependant package but another package also depends on this version
211 - this version has been merged as a duplicate with another version
212 - etc.
213
214 Due to the lack of necessary context, `uninstall` lifecycle scripts are not implemented and will not function.
215
216 ### User
217
218 When npm is run as root, scripts are always run with the effective uid and gid of the working directory owner.
219
220 ### Environment
221
222 Package scripts run in an environment where many pieces of information are made available regarding the setup of npm and the current state of the process.
223
224 #### path
225
226 If you depend on modules that define executable scripts, like test suites, then those executables will be added to the `PATH` for executing the scripts. So, if your package.json has this:
227
228 ```json
229 {
230 "name": "foo",
231 "dependencies": {
232 "bar": "0.1.x"
233 },
234 "scripts": {
235 "start": "bar ./test"
236 }
237 }
238 ```
239
240 then you could run `npm start` to execute the `bar` script, which is exported into the `node_modules/.bin` directory on `npm install`.
241
242 #### package.json vars
243
244 The package.json fields are tacked onto the `npm_package_` prefix. So, for instance, if you had `{"name":"foo", "version":"1.2.5"}` in your package.json file, then your package scripts would have the `npm_package_name` environment variable set to "foo", and the `npm_package_version` set to "1.2.5". You can access these variables in your code with `process.env.npm_package_name` and `process.env.npm_package_version`, and so on for other fields.
245
246 See [`package.json`](/cli/v9/configuring-npm/package-json) for more on package configs.
247
248 #### current lifecycle event
249
250 Lastly, the `npm_lifecycle_event` environment variable is set to whichever stage of the cycle is being executed. So, you could have a single script used for different parts of the process which switches based on what's currently happening.
251
252 Objects are flattened following this format, so if you had `{"scripts":{"install":"foo.js"}}` in your package.json, then you'd see this in the script:
253
254 ```bash
255 process.env.npm_package_scripts_install === "foo.js"
256 ```
257
258 ### Examples
259
260 For example, if your package.json contains this:
261
262 ```json
263 {
264 "scripts": {
265 "install": "scripts/install.js",
266 "postinstall": "scripts/install.js",
267 "uninstall": "scripts/uninstall.js"
268 }
269 }
270 ```
271
272 then `scripts/install.js` will be called for the install and post-install stages of the lifecycle, and `scripts/uninstall.js` will be called when the package is uninstalled. Since `scripts/install.js` is running for two different phases, it would be wise in this case to look at the `npm_lifecycle_event` environment variable.
273
274 If you want to run a make command, you can do so. This works just fine:
275
276 ```json
277 {
278 "scripts": {
279 "preinstall": "./configure",
280 "install": "make && make install",
281 "test": "make test"
282 }
283 }
284 ```
285
286 ### Exiting
287
288 Scripts are run by passing the line as a script argument to `sh`.
289
290 If the script exits with a code other than 0, then this will abort the process.
291
292 Note that these script files don't have to be Node.js or even JavaScript programs. They just have to be some kind of executable file.
293
294 ### Best Practices
295
296 - Don't exit with a non-zero error code unless you _really_ mean it. Except for uninstall scripts, this will cause the npm action to fail, and potentially be rolled back. If the failure is minor or only will prevent some optional features, then it's better to just print a warning and exit successfully.
297 - Try not to use scripts to do what npm can do for you. Read through [`package.json`](/cli/v9/configuring-npm/package-json) to see all the things that you can specify and enable by simply describing your package appropriately. In general, this will lead to a more robust and consistent state.
298 - Inspect the env to determine where to put things. For instance, if the `npm_config_binroot` environment variable is set to `/home/user/bin`, then don't try to install executables into `/usr/local/bin`. The user probably set it up that way for a reason.
299 - Don't prefix your script commands with "sudo". If root permissions are required for some reason, then it'll fail with that error, and the user will sudo the npm command in question.
300 - Don't use `install`. Use a `.gyp` file for compilation, and `prepare` for anything else. You should almost never have to explicitly set a preinstall or install script. If you are doing this, please consider if there is another option. The only valid use of `install` or `preinstall` scripts is for compilation which must be done on the target architecture.
301 - Scripts are run from the root of the package folder, regardless of what the current working directory is when `npm` is invoked. If you want your script to use different behavior based on what subdirectory you're in, you can use the `INIT_CWD` environment variable, which holds the full path you were in when you ran `npm run`.
302
303 ### See Also
304
305 - [npm run-script](/cli/v9/commands/npm-run-script)
306 - [package.json](/cli/v9/configuring-npm/package-json)
307 - [npm developers](/cli/v9/using-npm/developers)
308 - [npm install](/cli/v9/commands/npm-install)