Project: angular
Task (moderate):  1) Create services/blog.service.ts to manage related state (blog list and selected blog) in app.component.ts 2) When submit a new blog-form, check title duplication. Constraint: The duplication check code should be written in blog-form; 3) Add a span(.blog-list-len) near 'Hello Blog' in header.component.ts to show the length of blogs