env-emitter

Node.js module that adds event emitters to process.env. Requires no dependencies.

• Installation
• Usage
  • Listen for get events
  • Listen for set events
• More examples
  • Prevent any changes to process.env
  • Log warning for undefined vars

Installation

npm install env-emitter

Include the module at top of main file. This is only needed once in the application because it replaces the global process.env.

import 'env-emitter'

Usage

Listen for get events

import 'env-emitter'

process.env.on('get', event => {
    console.log(`Variable ${event.name} used at ${event.caller}`)
})

const test = process.env.FOO_BAR

// outputs: FOO_BAR used at /app/directory/file.js:7:13

event properties available:

• event.name
  • Name of variable accessed, such as NODE_ENV
• event.value
  • Value of variable accessed (or undefined)
• event.caller
  • String of where accessed, such as /app/directory/file.js:7:13
• event.callerIsCoreNode
  • Boolean, true if variable was accessed from a core Node module. This is helpful for filtering. Example being console.log() access lots of environment variables.

Listen for set events

import 'env-emitter'

process.env.on('set', event => {
    console.log(`Variable ${event.name} changed to ${event.newValue} at ${event.caller}`)
})

process.env.FOO_BAR = 'baz'

// outputs: FOO_BAR changed to baz at /app/directory/file.js:7:13

event properties available:

• event.name
  • Name of variable being changed, such as NODE_ENV
• event.caller
  • String of where variable is being changed, such as /app/directory/file.js:7:13
• event.previousValue
  • Value of variable BEFORE change (current value)
• event.newValue
  • Value of variable AFTER change (value after any listeners complete)

More examples

Prevent any changes to process.env

process.env.on('set', event => {
    throw new Error('Setting environment variables is not allowed')
})

Log warning for undefined vars

process.env.on('get', event => {
    // skip internal Node usage
    if (event.callerIsCoreNode) {
        return
    }   

    if (event.value === undefined) {
        console.log(`⚠️ ${event.name} at ${event.caller}`)
    }
})