Add task with the HTTP client
The TaskService
We just communicated with our API server to retrieve a list of tasks. Now we want to update the API server list by adding a new task.
Based on the HTTP protocol, we will use the post
function to add a task to the list.
As JSON-server is able to generate an id
for us, we will send a TaskForm
object to the server.
Open the src/app/task.service.ts
file.
Add the following code to the file:
This new addTask
function defines our contract with the API server:
- it makes a POST request
- it sends a
Task
object as a request body - it communicates with the API server at
http://localhost:3000/tasks
Update the TaskFormComponent
Open the src/app/task-form/task-form.component.ts
file.
Add the following code to the file:
By default an Observable is cold, meaning that the function will not be executed until we subscribe to it.
By using the async pipe to get the task list, we donβt need to subscribe to the getTasks
function in the TaskListComponent
.
Asynchronous programming
Letβs review the code we just changed in the submit
function of the TaskFormComponent
:
- We call the
addTask
function from theTaskService
to add a task to the API server. - We navigate to the
/tasks
route.
API communication is asynchronous, meaning that the addTask
function will not be executed immediately.
Our server is served locally, so the request will be fast, but itβs still asynchronous.
A request to the server can take a long time if the server or the network is slow for any reason.
In this situation, While the request is still being processed, the router.navigate
function will be executed.
Thatβs not what we want as by navigating, we want to display the updated task list.
We need to wait for the response from the server before navigating to the /tasks
route.
The Subscription
The subscribe function accepts a callback function as a parameter. This callback function will be executed when the observable emits a value.
Weβll use this callback function to navigate to the /tasks
route.
Open the src/app/task-form/task-form.component.ts
file.
Update the following code to the file:
βοΈ What you learned
In this chapter, you learned how to add a task to a list using the HTTP client in an Angular application.