## 原理
* 1、解析一个文件及其依赖
* 2、构建一个依赖关系图
* 3、将所有东西打包成一个单文件
## 代码实现
#### 文件结构
#### 1、解析文件及其依赖
通过babylon将文件解析成AST
[在线解析器](https://astexplorer.net/)：
代码实现：
bundle.js
```
const fs = require("fs");
const babylon = require("babylon");
const traverse = require("babel-traverse").default;
let ID = 0;
function createAsset(filename) {
const content = fs.readFileSync(filename, "utf-8");
// 解析文件成AST
const ast = babylon.parse(content, {
sourceType: "module",
});
const dependencies = [];
// 根据AST获取相关依赖
traverse(ast, {
ImportDeclaration: ({ node }) => {
dependencies.push(node.source.value);
},
});
const id = ID++;
return {
id,
filename,
dependencies,
};
}
const mainAssets = createAsset("./example/entry.js");
console.log(mainAssets)
```
输出结果：
#### 2、构建一个依赖关系图
```
// 构建一个依赖关系图
function createGraph(entry) {
const mainAssets = createAsset(entry);
const queue = [mainAssets];
for (const asset of queue) {
const dirname = path.dirname(asset.filename);
asset.mapping = {};
asset.dependencies.forEach((relativePath) => {
const absolutePath = path.join(dirname, relativePath);
const child = createAsset(absolutePath);
asset.mapping[relativePath] = child.id;
queue.push(child);
});
}
return queue;
}
const graph = createGraph("./example/entry.js");
console.log(graph);
```
输出结果：
#### 3、将所有东西打包成一个单文件
在解析文件时，使用babel对代码进行转译
```
// 解析一个文件及其依赖
function createAsset(filename) {
const content = fs.readFileSync(filename, "utf-8");
const ast = babylon.parse(content, {
sourceType: "module",
});
const dependencies = [];
traverse(ast, {
ImportDeclaration: ({ node }) => {
dependencies.push(node.source.value);
},
});
const id = ID++;
// 使用babel对代码进行转译
const { code } = babel.transformFromAst(ast, null, {
presets: ["env"],
});
return {
id,
filename,
dependencies,
code,
};
}
```
```
// 将所有东西打包成一个单文件
function bundle(graph) {
let modules = "";
graph.forEach((mod) => {
modules += `${mod.id}:[
function(require,module,exports){
${mod.code}
},
${JSON.stringify(mod.mapping)}
],`;
});
const result = `
(function(modules){
function require(id){
const [fn, mapping] = modules[id];
// 因为代码引入文件时根据相对路径，所以需要把相对路径跟id进行一个映射
function localRequire(relativePath){
return require(mapping[relativePath])
}
const module = {exports:{}};
fn(localRequire,module,module.exports)
return module.exports;
}
// 执行入口模块
require(0);
})({${modules}})
`;
return result;
}
const graph = createGraph("./example/entry.js");
const result = bundle(graph);
console.log(result);
```
输出结果：
```
(function(modules) {
function require(id) {
const [fn, mapping] = modules[id];
function localRequire(relativePath) {
return require(mapping[relativePath])
}
const module = {
exports: {}
};
fn(localRequire, module, module.exports)
return module.exports;
}
require(0);
})({
0: [
function(require, module, exports) {
"use strict";
var _message = require("./message.js");
var _message2 = _interopRequireDefault(_message);
function _interopRequireDefault(obj) {
return obj && obj.__esModule ? obj : {
default: obj
};
}
console.log(_message2.default);
},
{
"./message.js": 1
}
],
1: [
function(require, module, exports) {
"use strict";
Object.defineProperty(exports, "__esModule", {
value: true
});
var _name = require("./name.js");
exports.default = "hello " + _name.name + "!";
},
{
"./name.js": 2
}
],
2: [
function(require, module, exports) {
"use strict";
Object.defineProperty(exports, "__esModule", {
value: true
});
var name = exports.name = 'Aaron';
},
{}
],
})
```
把代码复制到浏览器运行，执行成功！
一个简易版的Webapck完成了。
## 相关链接
[例子源码](https://github.com/jiajunlin/Build-Your-Own-Webpack)
[视频教程](https://www.youtube.com/watch?v=Gc9-7PBqOC8)
[babylon](https://www.npmjs.com/package/babylon)
[babel-traverse docs](https://github.com/jamiebuilds/babel-handbook/blob/master/translations/en/plugin-handbook.md#babel-traverse)
