介绍升级从Ionic 4到Ionic 5时出现的问题（Angular）
首先
当将Ionic4升级到5时，能够顺利并没有问题地完成的人可能会比较少，不是吗？
当然，作为一个人也遇到了神秘的问题，感到困惑的家伙之一。
注意事项
这篇文章只是一个介绍所面临问题的文章，因此并没有详细介绍解决方案！尝试了很多命令后，坦率地说，没有一种强有力的信息可以断言“这个错误的解决方案就是这个！”。
升级之前的环境
Ionic:
Ionic CLI : 6.7.0 (/usr/local/lib/node_modules/@ionic/cli)
Ionic Framework : @ionic/angular 5.1.0
@angular-devkit/build-angular : 0.901.4
@angular-devkit/schematics : 8.1.3
@angular/cli : 8.1.3
@ionic/angular-toolkit : 2.2.0
Capacitor:
Capacitor CLI : 1.2.0
@capacitor/core : 1.2.0
Cordova:
Cordova CLI : 9.0.0 (cordova-lib@9.0.1)
Cordova Platforms : none
Cordova Plugins : no whitelisted plugins (0 plugins total)
Utility:
cordova-res (update available: 0.14.0) : 0.6.0
native-run (update available: 1.0.0) : 0.2.8
System:
NodeJS : v10.15.1 (/usr/local/bin/node)
npm : 6.12.1
OS : macOS Mojave
Xcode : Xcode 11.2.1 Build version 11B500
参考的網站
首先，我参考的网站有以下三个（尤其是以第二个为主）。
Ionic5已经推出。通过GIF动画介绍最新的Web移动UI框架！
将现有的Ionic 4.x 应用升级到 Ionic 5.x。
将Ionic 4升级到Ionic 5（Angular）。
错误1
将Ionic 4升级到Ionic 5（Angular）
执行此页面中提到的命令时发生
ng update @angular/cli@8 @angular/core@8 --allow-dirty
Repository is not clean. Update changes will be mixed with pre-existing changes.
Using package manager: 'npm'
Collecting installed dependencies...
Found 50 dependencies.
Fetching dependency metadata from registry...
Package "@angular-devkit/build-angular" has an incompatible peer dependency to "@angular/compiler-cli" (requires ">=9.0.0 < 10" (extended), would install "8.2.14").
Package "@angular-devkit/build-angular" has an incompatible peer dependency to "typescript" (requires ">=3.6 < 3.9", would install "3.5.3").
Incompatible peer dependencies found.
Peer dependency warnings when installing dependencies means that those dependencies might not work correctly together.
You can use the '--force' option to ignore incompatible peer dependencies and instead address these warnings later.
好的，不明白！
错误2
ng update @angular/core @angular/cli --allow-dirty
Your global Angular CLI version (9.1.4) is greater than your local
version (8.1.3). The local Angular CLI version is used.
To disable this warning use "ng config -g cli.warnings.versionMismatch false".
Repository is not clean. Update changes will be mixed with pre-existing changes.
Using package manager: 'npm'
Collecting installed dependencies...
Found 51 dependencies.
Fetching dependency metadata from registry...
Package "@angular/platform-browser" has a missing peer dependency of "@angular/animations" @ "9.1.4".
Incompatible peer dependencies found.
Peer dependency warnings when installing dependencies means that those dependencies might not work correctly together.
You can use the '--force' option to ignore incompatible peer dependencies and instead address these warnings later.
我知道全局的Angular CLI和本地的Angular CLI是不一样的，但是要怎么办呢？哈哈
错误3
ng update @angular/cli
Your global Angular CLI version (9.1.4) is greater than your local
version (8.1.3). The local Angular CLI version is used.
To disable this warning use "ng config -g cli.warnings.versionMismatch false".
Repository is not clean. Please commit or stash any changes before updating.
顺利运行的第一个命令
npm install --save-dev @angular/cli@latest
参考这个以后，明明一直都有出现这个下面的错误，不知道为什么用这个方法却奇迹般地成功了。。。
Your global Angular CLI version (9.1.4) is greater than your local
version (8.1.3). The local Angular CLI version is used.
To disable this warning use "ng config -g cli.warnings.versionMismatch false".
Repository is not clean. Please commit or stash any changes before updating.
执行此命令后，@angular/cli的数值发生改变了！
Ionic:
Ionic CLI : 6.7.0 (/usr/local/lib/node_modules/@ionic/cli)
Ionic Framework : @ionic/angular 5.1.0
@angular-devkit/build-angular : 0.901.4
@angular-devkit/schematics : 8.1.3
@angular/cli : 9.1.4
@ionic/angular-toolkit : 2.2.0
这是一个运行顺利的命令，第二个。
ng update @angular/cli @angular/core --allow-dirty
Repository is not clean. Please commit or stash any changes before updating.
在执行上述的ng update命令时，发生了这个错误。
通过参考这个并加上–allow-dirty选项，成功执行了。
最终/最后
不要放弃，尝试各种命令吧！我尝试了太多，完全记不得试了哪些命令了…
