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babel-plugin-lodash-extract

v0.0.3

Published

主要做的事情是按需加载lodash库 将如下的代码 ```javascript import _ from 'lodash' import isArray from 'lodash/isArray' import { toString } from 'lodash'

Downloads

2

Readme

简易的babel 插件开发入门例子

主要做的事情是按需加载lodash库 将如下的代码

import _ from 'lodash'
import isArray from 'lodash/isArray'
import { toString } from 'lodash'

isArray([])
_.add(1, 2)
toString(1)
_.add(1, 2)
isArray([1])

↓↓↓↓↓↓↓↓↓↓↓ 转换成如下的代码

import isArray from 'lodash/isArray';
import toString from 'lodash/toString';

isArray([]);
import add from 'lodash/add';
add(1, 2)

toString(1);
add(1, 2)

isArray([1]);

babel-plugin-lodash-extract

平常开发的时候有些同学会不遵守规范或者无意中使用了如下写法

import _ from 'lodash'
或
import loadsh from 'lodash'

这样会把所有的lodash代码都加载进去 导致大概js文件大小会大70kb左右

如下代码

import _ from 'lodash'

_.add(1, 2)

结果有71.1kb

static/js/vendor.6b317cc799badf6ad864.js    71.1 kB       0  [emitted]  vendor

但是这么写的话

import add from 'lodash/add'
add(1, 2)

发现只有这么大

static/js/vendor.d9f1fb9269405aa51217.js    2.24 kB       0  [emitted]  vendor

下载安装

npm i --save-dev babel-plugin-lodash-extract

示例:

在babel的配置文件里加上

{
  "plugins": ["babel-plugin-lodash-extract"],
}

这样的配置,这里需要注意是plugins的加载顺序是从后往前的,一般的项目都有添加 transform-runtime插件,那么写法需要这样

{
  "plugins": [
    "transform-runtime",
    "babel-plugin-lodash-extract"
  ],
}

CLI

  npm run test // unit test
  npm run debug // development debug
  npm run compile // development compile
  npm run example // run example

原理说明

首先根据babel的插件开发文档

发现所有的babel插件需要按照以下的格式来进行处理代码

module.exports = ({ types: t }) => {
  return {
    visitor: {
      // ...some code
    },
  };
}

然后babel会把你的代码解析成AST

首先建立一个目录example,里面建两个文件index.js, example.js

下列使用这个代码来进行处理

// example.js的内容

const a = 1 + 2;

↓↓↓↓↓↓↓↓ 解析成

const b = 2 - 3;

在这个网站https://astexplorer.net进行AST解析

观察一下这个语法树

首先进行变量a的替换 来看一下结果代码

module.exports = ({ types: t }) => {
  return {
    visitor: {
      Identifier(path) {
        if (path.node.name === 'a') {
          path.replaceWith(t.Identifier('b'));
        }
      },
    },
  };
}

// 在package.json里面加入 "example": "babel --plugins ../example/index.js ./example/example.js"
// 运行 npm run example
// 输出 const b = 1 + 2;

然后继续解析 1 + 2 -> 2 - 3

module.exports = ({ types: t }) => {
  return {
    visitor: {
      Identifier(path) {
        ...
      },
      BinaryExpression(path) {
        if (path.node.operator === '+') {
          const left = t.numericLiteral(2);
          const right = t.numericLiteral(3);
          path.replaceWith(t.binaryExpression('-', left, right));
        }
      }
    },
  };
}
// 输出 const b = 2 - 3;
// 目标完成

关于t上面有哪些方法可以根据__babel-types__的文档来进行查阅

还有__path__的一些使用方法在babel插件手册里也有部分解释

完整代码

module.exports = ({ types: t }) => {
  return {
    visitor: {
      Identifier(path) {
        if (path.node.name === 'a') {
          path.replaceWith(t.Identifier('b'));
        }
      },
      BinaryExpression(path) {
        if (path.node.operator === '+') {
          const left = t.numericLiteral(2);
          const right = t.numericLiteral(3);
          path.replaceWith(t.binaryExpression('-', left, right));
        }
      }
    },
  };
}

没了。