1、准备

克隆源码后，进入dotenv，读readme.md，按要求新建.env文件，并新建index.js文件，引入config.js文件，

NAME=若川
AGE=18
BLOG=https://lxchuan12.gitee.io
MP_WEIXIN='若川视野'
ACTIVITY="每周一起学200行左右的源码共读活动"
WEIXIN=加我微信 ruochuan12 参与

2、作用

读取 .env 文件
解析 .env 文件拆成键值对的对象形式
赋值到 process.env 上
最后返回解析后得到的对象

3、源码

1、config.js文件

(function () {
  // console.log("argv", process.argv);
  require("./lib/main").config(
    Object.assign(
      {},
      require("./lib/env-options"),
      require("./lib/cli-options")(process.argv)
    )
  );
})();
//合并options，做为main.js的config函数的参数

1、env-options.js

// ../config.js accepts options via environment variables
const options = {};
if (process.env.DOTENV_CONFIG_ENCODING != null) {
  options.encoding = process.env.DOTENV_CONFIG_ENCODING;
}

if (process.env.DOTENV_CONFIG_PATH != null) {
  options.path = process.env.DOTENV_CONFIG_PATH;
}

if (process.env.DOTENV_CONFIG_DEBUG != null) {
  options.debug = process.env.DOTENV_CONFIG_DEBUG;
}

if (process.env.DOTENV_CONFIG_OVERRIDE != null) {
  options.override = process.env.DOTENV_CONFIG_OVERRIDE;
}

module.exports = options;

2、cli-options.js

const re = /^dotenv_config_(encoding|path|debug|override)=(.+)$/

module.exports = function optionMatcher (args) {
  return args.reduce(function (acc, cur) {
    const matches = cur.match(re)
    if (matches) {
      acc[matches[1]] = matches[2]
    }
    return acc
  }, {})
}

2、main.js

const fs = require("fs");
const path = require("path");
const os = require("os");

const LINE =
  /(?:^|^)\s*(?:export\s+)?([\w.-]+)(?:\s*=\s*?|:\s+?)(\s*'(?:\'|[^'])*'|\s*"(?:\"|[^"])*"|\s*`(?:\`|[^`])*`|[^#\r\n]+)?\s*(?:#.*)?(?:$|$)/gm;

// Parser src into an Object
function parse(src) {
  const obj = {};
  // Convert buffer to string 将buffer变成字符串
  let lines = src.toString();

// Convert line breaks to same format 格式化字符串

lines = lines.replace(/\r\n?/gm, "\n"); // /r结束符 /n换行符 /gm 全局 m 多行匹配

let match;

while ((match = LINE.exec(lines)) != null) {

const key = match[1];

// Default undefined or null to empty string

let value = match[2] || "";

// Remove whitespace

value = value.trim();

// Check if double quoted

const maybeQuote = value[0]; //若

// Remove surrounding quotes //去掉双引号、单引号

value = value.replace(/^(['"`])([\s\S]*)\1 $/gm, "$ 2");

//$2 与 regexp 中的第 1 到第 99 个子表达式相匹配的文本

// Expand newlines if double quoted

if (maybeQuote === '"') {

value = value.replace(/\n/g, "\n");

value = value.replace(/\r/g, "\r");

}

// Add to object

obj[key] = value;

}

return obj;

}

function _log(message) {

console.log([dotenv][DEBUG] ${message});

}

function _resolveHome(envPath) {

return envPath[0] === "~"

? path.join(os.homedir(), envPath.slice(1))

: envPath;

}

// Populates process.env from .env file

function config(options) {

let dotenvPath = path.resolve(process.cwd(), ".env");

let encoding = "utf8";

const debug = Boolean(options && options.debug);

const override = Boolean(options && options.override);

if (options) {

if (options.path != null) {

dotenvPath = _resolveHome(options.path);

}

if (options.encoding != null) {

encoding = options.encoding;

}

try {

// Specifying an encoding returns a string instead of a buffer

const parsed = DotenvModule.parse(

fs.readFileSync(dotenvPath, { encoding })

);

console.log("parsed", parsed);

Object.keys(parsed).forEach(function (key) {

//判断key值是否属于process.env

if (!Object.prototype.hasOwnProperty.call(process.env, key)) {

process.env[key] = parsed[key];

} else {

if (override === true) {

process.env[key] = parsed[key];

}

if (debug) {

if (override === true) {

_log(

"${key}" is already defined in \process.env` and WAS overwritten`

);

} else {

_log(

"${key}" is already defined in \process.env` and was NOT overwritten`

);

}

});

return { parsed };

} catch (e) {

if (debug) {

_log(Failed to load ${dotenvPath} ${e.message});

}

return { error: e };

}

const DotenvModule = {

config,

parse,

};

module.exports.config = DotenvModule.config;

module.exports.parse = DotenvModule.parse;

module.exports = DotenvModule;

4、感谢

今天笔记写的有点乱但是按照了自己的理解写的看了7期源码很感谢若川老师不然我可能不会看源码通过源码学习了解了一些很高级的内容我不会去写的代码有很多感想但是今天有点忙哎呀接着冲最后真的很感谢若川老师

【若川视野 x 源码共读】第22期 | 项目中常用的 .env 文件原理是什么？如何实现？