How can I use variables in package.json?

Question

There is a feature from maven I miss a lot in package.json. In maven .pom file you can define variables in parent project and use them in child project\'s pom files.

Answer 1

Define a config object in package.json:

{
    "name"   : "myapp",
    "config" : { "port" : "3000" },
    ...
}

And then you can access port value from scrips object with $npm_package_config_port

{
    "name"   : "myapp",
    "config" : { "port" : "3000" },
    "scripts": {
        "start" : "node --harmony app.js $npm_package_config_port"
    },
    ...
}

The source full article is here:

http://www.marcusoft.net/2015/08/npm-scripting-configs-and-arguments.html#npm-configuration

Answer 2

Any key can be referenced, beginning with $npm_package_ and adding an underscore for every level you go down.

Example:

{ "name": "appname", "version": "0.0.1"}

name can be access like: $npm_package_name or ${npm_package_name} to delimit within string

For windows user, name can access like: %npm_package_name%

Answer 3

On Windows, you should use %variable_name%. For example:

{
   "name": "app_name",
   "version": "1.0.0",
   "custom": {
      "key": "any value"
   }
}

You can get it using %npm_package_name%, %npm_package_version% and %npm_package_custom_key%.