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Javascript

Asp Dot Net


This tutorial shows how to call an ASP.NET Core web API with JavaScript, using the
Fetch API
⁠
.

Prerequisites

Complete
Tutorial: Create a web API
⁠
⁠
Familiarity with CSS, HTML, and JavaScript

Call the web API with JavaScript

In this section, you'll add an HTML page containing forms for creating and managing to-do items. Event handlers are attached to elements on the page. The event handlers result in HTTP requests to the web API's action methods. The Fetch API's fetch function initiates each HTTP request.
The fetch function returns a
Promise
⁠
object, which contains an HTTP response represented as a Response object. A common pattern is to extract the JSON response body by invoking the json function on the Response object. JavaScript updates the page with the details from the web API's response.
The simplest fetch call accepts a single parameter representing the route. A second parameter, known as the init object, is optional. init is used to configure the HTTP request.

Configure the app to
serve static files
⁠
and
enable default file mapping
⁠
. The following highlighted code is needed in Program.cs:
C#
using Microsoft.EntityFrameworkCore;
using TodoApi.Models;

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddControllers();
builder.Services.AddDbContext<TodoContext>(opt =>
opt.UseInMemoryDatabase("TodoList"));

var app = builder.Build();

if (builder.Environment.IsDevelopment())
{
app.UseDeveloperExceptionPage();
}

app.UseDefaultFiles();
app.UseStaticFiles();

app.UseHttpsRedirection();

app.UseAuthorization();

app.MapControllers();

app.Run();


Create a wwwroot folder in the project root.
Create a css folder inside of the wwwroot folder.
Create a js folder inside of the wwwroot folder.
Add an HTML file named index.html to the wwwroot folder. Replace the contents of index.html with the following markup:
HTML


<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>To-do CRUD</title>
<link rel="stylesheet" href="css/site.css" />
</head>
<body>
<h1>To-do CRUD</h1>
<h3>Add</h3>
<form action="javascript:void(0);" method="POST" onsubmit="addItem()">
<input type="text" id="add-name" placeholder="New to-do">
<input type="submit" value="Add">
</form>

<div id="editForm">
<h3>Edit</h3>
<form action="javascript:void(0);" onsubmit="updateItem()">
<input type="hidden" id="edit-id">
<input type="checkbox" id="edit-isComplete">
<input type="text" id="edit-name">
<input type="submit" value="Save">
<a onclick="closeInput()" aria-label="Close">&#10006;</a>
</form>
</div>

<p id="counter"></p>

<table>
<tr>
<th>Is Complete?</th>
<th>Name</th>
<th></th>
<th></th>
</tr>
<tbody id="todos"></tbody>
</table>

<script src="js/site.js" asp-append-version="true"></script>
<script type="text/javascript">
getItems();
</script>
</body>
</html>

Add a CSS file named site.css to the wwwroot/css folder. Replace the contents of site.css with the following styles:
css
input[type='submit'], button, [aria-label] {
cursor: pointer;
}

#editForm {
display: none;
}

table {
font-family: Arial, sans-serif;
border: 1px solid;
border-collapse: collapse;
}

th {
background-color: #f8f8f8;
padding: 5px;
}

td {
border: 1px solid;
padding: 5px;
}


Add a JavaScript file named site.js to the wwwroot/js folder. Replace the contents of site.js with the following code:
JavaScript
const uri = 'api/todoitems';
let todos = [];

function getItems() {
fetch(uri)
.then(response => response.json())
.then(data => _displayItems(data))
.catch(error => console.error('Unable to get items.', error));
}

function addItem() {
const addNameTextbox = document.getElementById('add-name');

const item = {
isComplete: false,
name: addNameTextbox.value.trim()
};

fetch(uri, {
method: 'POST',
headers: {
'Accept': 'application/json',
'Content-Type': 'application/json'
},
body: JSON.stringify(item)
})
.then(response => response.json())
.then(() => {
getItems();
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