We just updated todo.Services.ts to call the Web API's GET action and fetch Todo items. Now, let's add code to post a new Todo item to the Web API. Follow the given steps to do so:

1. Open todo.service.ts.

2. Add the postTodo function that posts a new Todo item to the Web API controller:

     postTodo(todo: Todo): Promise<Todo> { 
             var headers = new Headers(); 
             headers.append('Content-Type',  
     'application/json'); 
        return this.http.post('/api/todos',  
     JSON.stringify(todo), { headers: headers }) 
            .toPromise() 
            .then(response => response.json() as Todo) 
            .catch(this.handleError); 
     } 

This function accepts a Todo item as an argument. It defines the header section with the JSON content type and posts the Todo item using the http service to a Web API asynchronously. The response is converted to Promise and the then method returns a Promise<Todo>.