Add an HTML file named
index.html
to the
wwwroot
folder. Replace the contents of
index.html
with the following markup:
<!DOCTYPE html>
<meta charset="UTF-8">
<title>To-do CRUD</title>
<link rel="stylesheet" href="css/site.css" />
</head>
<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">✖</a>
</form>
<p id="counter"></p>
<table>
<th>Is Complete?</th>
<th>Name</th>
<th></th>
<th></th>
<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:
input[type='submit'], button, [aria-label] {
cursor: pointer;
#editForm {
display: none;
table {
font-family: Arial, sans-serif;
border: 1px solid;
border-collapse: collapse;
background-color: #f8f8f8;
padding: 5px;
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:
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();
addNameTextbox.value = '';
.catch(error => console.error('Unable to add item.', error));
function deleteItem(id) {
fetch(`${uri}/${id}`, {
method: 'DELETE'
.then(() => getItems())
.catch(error => console.error('Unable to delete item.', error));
function displayEditForm(id) {
const item = todos.find(item => item.id === id);
document.getElementById('edit-name').value = item.name;
document.getElementById('edit-id').value = item.id;
document.getElementById('edit-isComplete').checked = item.isComplete;
document.getElementById('editForm').style.display = 'block';
function updateItem() {
const itemId = document.getElementById('edit-id').value;
const item = {
id: parseInt(itemId, 10),
isComplete: document.getElementById('edit-isComplete').checked,
name: document.getElementById('edit-name').value.trim()
fetch(`${uri}/${itemId}`, {
method: 'PUT',
headers: {
'Accept': 'application/json',
'Content-Type': 'application/json'
body: JSON.stringify(item)
.then(() => getItems())
.catch(error => console.error('Unable to update item.', error));
closeInput();
return false;
function closeInput() {
document.getElementById('editForm').style.display = 'none';
function _displayCount(itemCount) {
const name = (itemCount === 1) ? 'to-do' : 'to-dos';
document.getElementById('counter').innerText = `${itemCount} ${name}`;
function _displayItems(data) {
const tBody = document.getElementById('todos');
tBody.innerHTML = '';
_displayCount(data.length);
const button = document.createElement('button');
data.forEach(item => {
let isCompleteCheckbox = document.createElement('input');
isCompleteCheckbox.type = 'checkbox';
isCompleteCheckbox.disabled = true;
isCompleteCheckbox.checked = item.isComplete;
let editButton = button.cloneNode(false);
editButton.innerText = 'Edit';
editButton.setAttribute('onclick', `displayEditForm(${item.id})`);
let deleteButton = button.cloneNode(false);
deleteButton.innerText = 'Delete';
deleteButton.setAttribute('onclick', `deleteItem(${item.id})`);
let tr = tBody.insertRow();
let td1 = tr.insertCell(0);
td1.appendChild(isCompleteCheckbox);
let td2 = tr.insertCell(1);
let textNode = document.createTextNode(item.name);
td2.appendChild(textNode);
let td3 = tr.insertCell(2);
td3.appendChild(editButton);
let td4 = tr.insertCell(3);
td4.appendChild(deleteButton);
todos = data;
A change to the ASP.NET Core project's launch settings may be required to test the HTML page locally:
Open Properties\launchSettings.json.
Remove the launchUrl
property to force the app to open at index.html
—the project's default file.
This sample calls all of the CRUD methods of the web API. Following are explanations of the web API requests.
Get a list of to-do items
In the following code, an HTTP GET request is sent to the api/todoitems route:
fetch(uri)
.then(response => response.json())
.then(data => _displayItems(data))
.catch(error => console.error('Unable to get items.', error));
When the web API returns a successful status code, the _displayItems
function is invoked. Each to-do item in the array parameter accepted by _displayItems
is added to a table with Edit and Delete buttons. If the web API request fails, an error is logged to the browser's console.
Add a to-do item
In the following code:
An item
variable is declared to construct an object literal representation of the to-do item.
A Fetch request is configured with the following options:
method
—specifies the POST HTTP action verb.
body
—specifies the JSON representation of the request body. The JSON is produced by passing the object literal stored in item
to the JSON.stringify function.
headers
—specifies the Accept
and Content-Type
HTTP request headers. Both headers are set to application/json
to specify the media type being received and sent, respectively.
An HTTP POST request is sent to the api/todoitems route.
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();
addNameTextbox.value = '';
.catch(error => console.error('Unable to add item.', error));
When the web API returns a successful status code, the getItems
function is invoked to update the HTML table. If the web API request fails, an error is logged to the browser's console.
Update a to-do item
Updating a to-do item is similar to adding one; however, there are two significant differences:
The route is suffixed with the unique identifier of the item to update. For example, api/todoitems/1.
The HTTP action verb is PUT, as indicated by the method
option.
fetch(`${uri}/${itemId}`, {
method: 'PUT',
headers: {
'Accept': 'application/json',
'Content-Type': 'application/json'
body: JSON.stringify(item)
.then(() => getItems())
.catch(error => console.error('Unable to update item.', error));
Delete a to-do item
To delete a to-do item, set the request's method
option to DELETE
and specify the item's unique identifier in the URL.
fetch(`${uri}/${id}`, {
method: 'DELETE'
.then(() => getItems())
.catch(error => console.error('Unable to delete item.', error));
Advance to the next tutorial to learn how to generate web API help pages:
Get started with Swashbuckle and ASP.NET Core
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 the Configure
method of Startup.cs
:
public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
if (env.IsDevelopment())
app.UseDeveloperExceptionPage();
app.UseDefaultFiles();
app.UseStaticFiles();
app.UseHttpsRedirection();
app.UseRouting();
app.UseAuthorization();
app.UseEndpoints(endpoints =>
endpoints.MapControllers();
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:
<!DOCTYPE html>
<meta charset="UTF-8">
<title>To-do CRUD</title>
<link rel="stylesheet" href="css/site.css" />
</head>
<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">✖</a>
</form>
<p id="counter"></p>
<table>
<th>Is Complete?</th>
<th>Name</th>
<th></th>
<th></th>
<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:
input[type='submit'], button, [aria-label] {
cursor: pointer;
#editForm {
display: none;
table {
font-family: Arial, sans-serif;
border: 1px solid;
border-collapse: collapse;
background-color: #f8f8f8;
padding: 5px;
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:
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();
addNameTextbox.value = '';
.catch(error => console.error('Unable to add item.', error));
function deleteItem(id) {
fetch(`${uri}/${id}`, {
method: 'DELETE'
.then(() => getItems())
.catch(error => console.error('Unable to delete item.', error));
function displayEditForm(id) {
const item = todos.find(item => item.id === id);
document.getElementById('edit-name').value = item.name;
document.getElementById('edit-id').value = item.id;
document.getElementById('edit-isComplete').checked = item.isComplete;
document.getElementById('editForm').style.display = 'block';
function updateItem() {
const itemId = document.getElementById('edit-id').value;
const item = {
id: parseInt(itemId, 10),
isComplete: document.getElementById('edit-isComplete').checked,
name: document.getElementById('edit-name').value.trim()
fetch(`${uri}/${itemId}`, {
method: 'PUT',
headers: {
'Accept': 'application/json',
'Content-Type': 'application/json'
body: JSON.stringify(item)
.then(() => getItems())
.catch(error => console.error('Unable to update item.', error));
closeInput();
return false;
function closeInput() {
document.getElementById('editForm').style.display = 'none';
function _displayCount(itemCount) {
const name = (itemCount === 1) ? 'to-do' : 'to-dos';
document.getElementById('counter').innerText = `${itemCount} ${name}`;
function _displayItems(data) {
const tBody = document.getElementById('todos');
tBody.innerHTML = '';
_displayCount(data.length);
const button = document.createElement('button');
data.forEach(item => {
let isCompleteCheckbox = document.createElement('input');
isCompleteCheckbox.type = 'checkbox';
isCompleteCheckbox.disabled = true;
isCompleteCheckbox.checked = item.isComplete;
let editButton = button.cloneNode(false);
editButton.innerText = 'Edit';
editButton.setAttribute('onclick', `displayEditForm(${item.id})`);
let deleteButton = button.cloneNode(false);
deleteButton.innerText = 'Delete';
deleteButton.setAttribute('onclick', `deleteItem(${item.id})`);
let tr = tBody.insertRow();
let td1 = tr.insertCell(0);
td1.appendChild(isCompleteCheckbox);
let td2 = tr.insertCell(1);
let textNode = document.createTextNode(item.name);
td2.appendChild(textNode);
let td3 = tr.insertCell(2);
td3.appendChild(editButton);
let td4 = tr.insertCell(3);
td4.appendChild(deleteButton);
todos = data;
A change to the ASP.NET Core project's launch settings may be required to test the HTML page locally:
Open Properties\launchSettings.json.
Remove the launchUrl
property to force the app to open at index.html
—the project's default file.
This sample calls all of the CRUD methods of the web API. Following are explanations of the web API requests.
Get a list of to-do items
In the following code, an HTTP GET request is sent to the api/todoitems route:
fetch(uri)
.then(response => response.json())
.then(data => _displayItems(data))
.catch(error => console.error('Unable to get items.', error));
When the web API returns a successful status code, the _displayItems
function is invoked. Each to-do item in the array parameter accepted by _displayItems
is added to a table with Edit and Delete buttons. If the web API request fails, an error is logged to the browser's console.
Add a to-do item
In the following code:
An item
variable is declared to construct an object literal representation of the to-do item.
A Fetch request is configured with the following options:
method
—specifies the POST HTTP action verb.
body
—specifies the JSON representation of the request body. The JSON is produced by passing the object literal stored in item
to the JSON.stringify function.
headers
—specifies the Accept
and Content-Type
HTTP request headers. Both headers are set to application/json
to specify the media type being received and sent, respectively.
An HTTP POST request is sent to the api/todoitems route.
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();
addNameTextbox.value = '';
.catch(error => console.error('Unable to add item.', error));
When the web API returns a successful status code, the getItems
function is invoked to update the HTML table. If the web API request fails, an error is logged to the browser's console.
Update a to-do item
Updating a to-do item is similar to adding one; however, there are two significant differences:
The route is suffixed with the unique identifier of the item to update. For example, api/todoitems/1.
The HTTP action verb is PUT, as indicated by the method
option.
fetch(`${uri}/${itemId}`, {
method: 'PUT',
headers: {
'Accept': 'application/json',
'Content-Type': 'application/json'
body: JSON.stringify(item)
.then(() => getItems())
.catch(error => console.error('Unable to update item.', error));
Delete a to-do item
To delete a to-do item, set the request's method
option to DELETE
and specify the item's unique identifier in the URL.
fetch(`${uri}/${id}`, {
method: 'DELETE'
.then(() => getItems())
.catch(error => console.error('Unable to delete item.', error));
Advance to the next tutorial to learn how to generate web API help pages:
Get started with Swashbuckle and ASP.NET Core