细说webpack源码之compile流程-rules参数处理技巧(2)

上篇文章给大家介绍了细说webpack源码之compile流程-rules参数处理技巧(1)，    细说webpack源码之compile流程-入口函数run

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第一步处理rule为字符串，直接返回一个包装类，很简单看注释就好了。

test

　　然后处理test、include、exclude，如下：

if (rule.test || rule.include || rule.exclude) { // 标记使用参数 checkResourceSource("test + include + exclude"); // 没有就是undefined condition = { test: rule.test, include: rule.include, exclude: rule.exclude }; // 处理常规参数 try { newRule.resource = RuleSet.normalizeCondition(condition); } catch (error) { throw new Error(RuleSet.buildErrorMessage(condition, error)); }}

　　checkResourceSource直接看源码：

let resourceSource;// ...function checkResourceSource(newSource) { // 第一次直接跳到后面赋值 if (resourceSource && resourceSource !== newSource) throw new Error(RuleSet.buildErrorMessage(rule, new Error("Rule can only have one resource source (provided " + newSource + " and " + resourceSource + ")"))); resourceSource = newSource;}

　　这个用于检测配置来源的唯一性，后面会能看到作用，同样作用的还有checkUseSource方法。

　　随后将三个参数包装成一个对象传入normalizeCondition方法，该方法对常规参数进行函数包装：

class RuleSet { constructor(rules) { /**/ }; static normalizeCondition(condition) { // 假值报错 if (!condition) throw new Error("Expected condition but got falsy value"); // 检测给定字符串是否以这个开头 if (typeof condition === "string") { return str => str.indexOf(condition) === 0; } // 函数直接返回 if (typeof condition === "function") { return condition; } // 正则表达式返回一个正则的test函数 if (condition instanceof RegExp) { return condition.test.bind(condition); } // 数组map递归处理 有一个满足返回true if (Array.isArray(condition)) {  const items = condition.map(c => RuleSet.normalizeCondition(c));  return orMatcher(items); } if (typeof condition !== "object") throw Error("Unexcepted " + typeof condition + " when condition was expected (" + condition + ")"); const matchers = []; // 对象会对每个值进行函数包装弹入matchers中 Object.keys(condition).forEach(key => {  const value = condition[key];  switch (key) {  case "or":  case "include":  case "test":   if (value)   matchers.push(RuleSet.normalizeCondition(value));   break;  case "and":   if (value) {   const items = value.map(c => RuleSet.normalizeCondition(c));   matchers.push(andMatcher(items));   }   break;  case "not":  case "exclude":   if (value) {   const matcher = RuleSet.normalizeCondition(value);   matchers.push(notMatcher(matcher));   }   break;  default:   throw new Error("Unexcepted property " + key + " in condition");  } }); if (matchers.length === 0)  throw new Error("Excepted condition but got " + condition); if (matchers.length === 1)  return matchers[0]; return andMatcher(matchers); }}