我刚刚将我的 Angular 5 项目升级到 Angular 6。升级后编译正常，但网站显示空白。在控制台中我得到:
Current document does not have a doctype. This may cause some Angular Material components not to behave as expected. push../node_modules/@angular/material/esm5/core.es5.js.MatCommonModule._checkDoctypeIsDefined @ core.es5.js:127 MatCommonModule @ core.es5.js:92 _createClass @ core.js:8116 createProviderInstance$1 @ core.js:8088 initNgModule @ core.js:8024 NgModuleRef @ core.js:8747 createNgModuleRef @ core.js:8736 debugCreateNgModuleRef @ core.js:10561 push../node_modules/@angular/core/fesm5/core.js.NgModuleFactory_.create @ core.js:11263 (anonymous) @ core.js:4161 push../node_modules/zone.js/dist/zone.js.ZoneDelegate.invoke @ zone.js:388 onInvoke @ core.js:3671 push../node_modules/zone.js/dist/zone.js.ZoneDelegate.invoke @ zone.js:387 push../node_modules/zone.js/dist/zone.js.Zone.run @ zone.js:138 push../node_modules/@angular/core/fesm5/core.js.NgZone.run @ core.js:3585 push../node_modules/@angular/core/fesm5/core.js.PlatformRef.bootstrapModuleFactory @ core.js:4159 (anonymous) @ core.js:4200 push../node_modules/zone.js/dist/zone.js.ZoneDelegate.invoke @ zone.js:388 push../node_modules/zone.js/dist/zone.js.Zone.run @ zone.js:138 (anonymous) @ zone.js:872 push../node_modules/zone.js/dist/zone.js.ZoneDelegate.invokeTask @ zone.js:421 push../node_modules/zone.js/dist/zone.js.Zone.runTask @ zone.js:188 drainMicroTaskQueue @ zone.js:595 Promise.then (async)
scheduleMicroTask @ zone.js:578 push../node_modules/zone.js/dist/zone.js.ZoneDelegate.scheduleTask @ zone.js:410 push../node_modules/zone.js/dist/zone.js.Zone.scheduleTask @ zone.js:232 push../node_modules/zone.js/dist/zone.js.Zone.scheduleMicroTask @ zone.js:252 scheduleResolveOrReject @ zone.js:862 ZoneAwarePromise.then @ zone.js:962 push../node_modules/@angular/core/fesm5/core.js.PlatformRef.bootstrapModule @ core.js:4200 ./src/main.ts @ main.ts:12 webpack_require @ bootstrap:76 0 @ main.ts:13 webpack_require @ bootstrap:76 checkDeferredModules @ bootstrap:43 webpackJsonpCallback @ bootstrap:30 (anonymous)TypeError: Cannot read property 'appendChild' of null at MatCommonModule.push../node_modules/@angular/material/esm5/core.es5.js.MatCommonModule._checkThemeIsPresent (core.es5.js:141) at new MatCommonModule (core.es5.js:93) at _createClass (core.js:8116) at createProviderInstance$1 (core.js:8088) at initNgModule (core.js:8024) at new NgModuleRef (core.js:8747) at createNgModuleRef (core.js:8736) at Object.debugCreateNgModuleRef [as createNgModuleRef] (core.js:10561) at NgModuleFactory_.push../node_modules/@angular/core/fesm5/core.js.NgModuleFactory_.create (core.js:11263) at core.js:4161
这是 @angular/material 有问题，还是项目中有什么地方没有正确升级？
如果我可以添加任何内容来帮助诊断，请告诉我。
最佳答案
如果你想删除这个警告，只需在你的通用 index.html 文件的顶部添加一个 Doctype，就像这样:
<!doctype html>
<html lang="en">
<head>
...
</html>
关于angular - 从 Angular 5 升级到 Angular 6 后 : Current document does not have a doctype，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/50768703/