Webpack Error——TypeError: Cannot read property 'properties' of undefined原因分析及解決方法

一、背景

使用webpack構建項目時報錯：

                                describe: optionsSchema.definitions.output.properties.path.description,
                                                                           ^
TypeError: Cannot read property 'properties' of undefined
    at module.exports (D:\00_git_pull\Mindsphere-Ali\Starter-Service\FleetManager-Lynn\fleetmanager\node_modules\webpack-cli\bin\config-yargs.js:89:48)
    at Object.<anonymous> (D:\00_git_pull\Mindsphere-Ali\Starter-Service\FleetManager-Lynn\fleetmanager\node_modules\webpack-dev-server\bin\webpack-dev-server.js:84:40)
    at Module._compile (internal/modules/cjs/loader.js:689:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:700:10)
    at Module.load (internal/modules/cjs/loader.js:599:32)
    at tryModuleLoad (internal/modules/cjs/loader.js:538:12)
    at Function.Module._load (internal/modules/cjs/loader.js:530:3)
    at Function.Module.runMain (internal/modules/cjs/loader.js:742:12)
    at startup (internal/bootstrap/node.js:279:19)
    at bootstrapNodeJSCore (internal/bootstrap/node.js:696:3)

二、 原因分析

根據報錯，可以發現，報錯出現在項目文件夾下的node_modules\webpack-cli\bin\config-yargs.js文件 第89行。

// webpack-cli 2.1.3 config-yargs.js
			"output-path": {
				type: "string",
				describe: optionsSchema.definitions.output.properties.path.description, //報錯
				group: OUTPUT_GROUP,
				defaultDescription: "The current directory",
				requiresArg: true
			},

當前webpack-cli的版本爲2.1.3，當前webpack版本爲4.20.2。查看webpack 的release log，發現

注意： webpack4.20.0以上版本要使用3.1.1版本的webpack-cli

webpack4.20.0發行日志: https://github.com/webpack/webpack/releases/tag/v4.20.0

三、解決辦法

更新webpack-cli到3.1.1及以上版本，執行npm i webpack-cli；

+ webpack-cli@3.1.2
updated 1 package and audited 22855 packages in 18.32s

安裝最新版3.1.2版本webpacl-cli後，output-path變爲

			"output-path": {
				type: "string",
				describe: getSchemaInfo("output.path", "description"), //更新部分
				group: OUTPUT_GROUP,
				defaultDescription: "The current directory",
				requiresArg: true
			},

再次執行webpack命令打包運行項目，done。

i ｢wds｣: Project is running at http://localhost:3000/webpack-dev-server/
i ｢wds｣: webpack output is served from /
i ｢wds｣: Content not from webpack is served from D:\00_git_pull\Mindsphere-Ali\Starter-Service\FleetManager-Lynn\fleetmanager\resources\
i ｢wdm｣: Compiled successfully.