1. providedIn property of the @Injectable() to "root".
2. Include the service in the AppModule or in a module that is only imported by the AppModule
https://angular.io/guide/singleton-services
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NetCore : webApi + angular + angular Material
mat-menu : https://material.angular.io/components/menu/overview
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來貢獻一下，順便試試OpenLayers : https://openlayers.org/
source : https://data.gov.tw/dataset/116285
https://github.com/kiang/pharmacies 感謝前輩提供藥局(經緯度) api
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Service : https://angular.io/guide/architecture-services
將服務拿來使用公用，Property、Fun
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