Node.js - read .env file (custom solution)
In this short article, we would like to show some custom implementaion that lets to read environment variables from .env file under Node.js.
The below implementation provides the following API:
Constants:
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property that contains default env file name ( |
Functions:
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function that reads
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function that reads
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Project structure:
xxxxxxxxxx/opt/my-website/ ├─ frontend/ └─ backend/ ├─ index.js ├─ env.js └─ .env
Example index.js file:
xxxxxxxxxxconst {initializeVariables, ENV_PATH} = require('./env');const ENV_CONSTANTS = { __dirname: () => __dirname, // use it in `.env` file as %__dirname% __filename: () => __filename // use it in `.env` file as %__filename%};initializeVariables(ENV_PATH, ENV_CONSTANTS); // ENV_CONSTANTS enables constant values injection (we can use e.g. VARIABLE_NAME=%CONSTANT_NAME%)console.log(process.env.BACKEND_PATH);console.log(process.env.FRONTEND_PATH);Note:
When you use
__dirnameor__filenameinENV_CONSTANTSbe sure what values are returned. It is recommended to createENV_CONSTANTSobject and read.envfile inindex.jsfile in the project root directory.
Example output:
xxxxxxxxxx/opt/my-website/backend/opt/my-website/frontend
Example .env file:
xxxxxxxxxxAPPLICATION_PATH=%__dirname%BACKEND_PATH=$APPLICATION_PATH$/backendFRONTEND_PATH=$APPLICATION_PATH$/frontend
Example env.js file:
xxxxxxxxxxconst fs = require('fs');const NEWLINE_EXPRESSION = /\r?\n/g;// Syntax://// %NODE_CONSTANT_NAME% - constant defined in application source code// $LOCAL_VARIABLE_NAME$ - variable defined in `.env` file// *GLOBAL_VARIABLE_NAME* - variable defined in `process.env` object//const REFERENCE_EXPRESSION = /%%|%([^%*$]+)%|%|\*\*|\*([^%*$]+)\*|\*|\$\$|\$([^%*$]+)\$|\$/g;const ENV_PATH = exports.ENV_PATH = '.env';const iterateVariables = exports.iterateVariables = (text, callback) => { const lines = text.split(NEWLINE_EXPRESSION); for (let i = 0; i < lines.length; ++i) { const line = lines[i]; if (line) { const index = line.indexOf('='); if (index !== -1) { const name = line.substring(0, index); if (name) { const value = line.substring(index + 1); callback(name, value, i); } } } }};const readVariables = exports.readVariables = (path = ENV_PATH, constants = {}) => { const text = fs.readFileSync(path, 'utf-8'); const variables = []; const environment = process.env; iterateVariables(text, (name, value, index) => { const action = (match, group1, group2, group3) => { switch (match) { case '%': throw new Error(`Incorrect '%' character usage in 'name=${value}' line (line number: ${index + 1}).`); case '*': throw new Error(`Incorrect '*' character usage in 'name=${value}' line (line number: ${index + 1}).`); case '$': throw new Error(`Incorrect '$' character usage in 'name=${value}' line (line number: ${index + 1}).`); case '%%': return '%'; case '**': return '*'; case '$$': return '$'; default: switch (match[0]) { case '%': { const constant = constants[group1]; if (constant) { return constant(); } throw new Error(`Unknown '%${group1}%' environment constant.`); } case '*': { const variable = environment[group2]; if (variable == null) { // null or undefined throw new Error(`Unknown '%${group2}%' environment variable.`); } return variable; } case '$': { const variable = variables[group3]; if (variable == null) { // null or undefined throw new Error(`Unknown '$${group3}$' environment variable.`); } return variable; } default: throw new Error(`Unknown constant/variable type.`); } } }; variables[name] = value.replace(REFERENCE_EXPRESSION, action); }); return variables;};const initializeVariables = exports.initializeVariables = (path = ENV_PATH, constants = null) => { const variables = readVariables(path, constants); const keys = Object.keys(variables); for (const key of keys) { process.env[key] = variables[key]; }};
