@kitajs/html
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@kitajs/html is a super fast JSX runtime to generate HTML strings that works everywhere.
AdonisJS? Express? Fastify? Hono? Bun? Htmx?
If your code works with strings, we got you covered.
To use the @kitajs/html package, follow these steps:
Install the required npm packages, @kitajs/html and @kitajs/ts-html-plugin, to
enable editor intellisense. Open your terminal and run:
npm install @kitajs/html @kitajs/ts-html-plugin
Configure your TypeScript project to transpile TSX/JSX into JavaScript and using our
LSP Plugin. Update your tsconfig.json file with
the following settings:
// tsconfig.json
{
"compilerOptions": {
"jsx": "react-jsx",
"jsxImportSource": "@kitajs/html",
"plugins": [{ "name": "@kitajs/ts-html-plugin" }]
}
}
Append the
xss-scan
command into your test script. This CLI comes from @kitajs/ts-html-plugin, which
catches XSS vulnerabilities that may be introduced into your codebase, automating the
xss scanning process to run everytime you test your code, like inside your CI/CD
environment. Open your package.json file and add the following script:
// package.json
{
"scripts": {
"test": "xss-scan"
}
}
Ensure that your code editor is using the TypeScript version from your project's
node_modules instead of the globally installed TypeScript. For Visual Studio Code,
you can configure this in your workspace settings:
// .vscode/settings.json
{
"typescript.tsdk": "node_modules/typescript/lib",
"typescript.enablePromptUseWorkspaceTsdk": true
}
[!CAUTION]
Be sure your setup is working correclty!
Try writing
console.log(<div>{String.name}</div>);in your editor. If it THROWS aXSSerror, then your setup is correct. Refer to the @kitajs/ts-html-plugin repository for more details on setting up editor intellisense. (It should throw, asString.namehas a type ofstring, type which may or may not have special caracters)
After installing the @kitajs/html package and configuring your TypeScript project, you
should be able to use JSX to generate HTML inside your .tsx files.
const html = (
<div>
<h1>Hello, world!</h1>
<p>Welcome to the KitaJS HTML package.</p>
</div>
);
Always use the safe attribute or manually call Html.escapeHtml to protect against XSS
vulnerabilities when rendering user input.
Ensuring XSS prevention is vital to guarantee your application's security. You can employ
the
@kitajs/ts-html-plugin
to catch XSS issues in your code editor and enhance your code's security.
[!IMPORTANT]
Please utilize our@kitajs/ts-html-pluginto emit TypeScript errors wherever you are exposed to XSS. Refer to Getting Started for installation instructions.
This package sanitizes every attribute by default. However, since the resulting element is
always a string, it's impossible to differentiate an HTML element created by a <tag> or
from user input. This necessitates the use of the provided safe
or manual invocation of Html.escapeHtml. Or you can also use the Html.escape or its
alias e template function.
import { e } from '@kitajs/html';
<div>⚠️ This will NOT be escaped and WILL expose you to XSS</div>
<div attr="This WILL be escaped"></div>
<div safe>This WILL be escaped</div>
<div>{Html.escapeHtml('This WILL be escaped')}</div>
<div>{e`This WILL be escaped: ${someVar}`}</div>
Here's an example of how this is DANGEROUS for your application:
user = {
name: 'Bad guy',
description: '</div><script>getStoredPasswordAndSentToBadGuysServer()</script>'
};
// Executes malicious code:
input = <div class="user-card">{user.description}</div>;
output = (
<div class="user-card">
<script>getStoredPasswordAndSentToBadGuysServer()</script>
</div>
);
// Does not execute any malicious code:
input = (
<div class="user-card" safe>
{user.description}
</div>
);
output = (
<div class="user-card">
</div><script>getStoredPasswordAndSentToBadGuysServer()</script>
</div>
);
Always use the safe attribute when rendering uncontrolled user input. This will sanitize
the contents and prevent XSS attacks.
function UserCard({ name, description, date, about }) {
return (
<div class="card">
<h1 safe>{name}</h1>
<br />
<p safe>{description}</p>
<br />
// Controlled input, no need to sanitize
<time datetime={date.toISOString()}>{date.toDateString()}</time>
<br />
<p safe>{about}</p>
</div>
);
}
Note that you should only use the safe attribute at the very bottom of the HTML tree
where it's needed.
Note: This section has been relocated to the @kitajs/ts-html-plugin repository.
Please consult their "Getting Started" section for instructions on enabling editor IntelliSense and using the CLI tool.
Async components are supported. When any child or sub child of a component tree is a promise, the whole tree will return a promise of the html string.
If no async components are found, the result will be simply a string, and you can safely cast it into a string.
async function Async() {
await callApi();
return <div>Async!</div>;
}
function Sync() {
return <div>Sync!</div>;
}
const async = (
<div>
<Async />
</div>
);
async instanceof Promise;
const sync: string = (
<div>
<Sync />
</div>
);
typeof sync === 'string';
A JSX.Element will always be a string. Once a children element is a async component, the
entire upper tree will also be async.
Learn when JSX.Element is a Promise.
The only problem when rendering templates is that you must wait for the whole template to be rendered before sending it to the client. This is not a problem for small templates, but it can be a problem for large templates.
To solve this problem, we provide a Suspense component that combined with
renderToStream() rendering method, will stream a fallback component while it waits for
his children to be rendered. This is a perfect combo to use with
async components.
import { Suspense, renderToStream } from '@kitajs/html/suspense';
async function MyAsyncComponent() {
const data = await database.query();
return <User name={data.username} />;
}
function renderUserPage(rid: number) {
return (
<Suspense
rid={rid}
fallback={<div>Loading username...</div>}
catch={(err) => <div>Error: {err.stack}</div>}
>
<MyAsyncComponent />
</Suspense>
);
}
// Html is a string readable stream that can be piped to the client
const html = renderToStream(renderUserPage);
[!NOTE]
TherenderToStream()is returns a native node/bun stream, head over to our suspense-server example to see how to use it with node:http, Express or Fastify servers.
The above example would render <div>Loading username...</div> while waiting for the
MyAsyncComponent to be rendered.
When using Suspense, you cannot just call the component and get the html string, you
need to use the renderToStream function to get a stream that can be piped to the client
with updates. Otherwise, the fallback would render forever.
As the result of any JSX component is always a string, you must use the rid provided by
renderToStream into all your suspense components, this way we can identify which
suspense is for which request and be able to render concurrent requests.
Suspense also accepts async fallbacks, but it blocks rendering until the fallback is resolved.
function renderTemplate(rid: number) {
return (
<Suspense
rid={rid}
fallback={<MyAsyncFallback />}
catch={(err) => <div>Error: {err.stack}</div>}
>
<MyAsyncComponent />
</Suspense>
);
}
The above example would only return anything after MyAsyncFallback is resolved. To catch
async fallback errors, you must wrap it into a ErrorBoundary.
The same way as promises must be awaited to resolve its own html, errors must be caught. Outside of suspense components, you can use the provided error boundaries to catch errors.
import { ErrorBoundary } from '@kitajs/html/error-boundary';
async function MyAsyncComponent() {
const data = await database.query(); // this promise may reject
return <User name={data.username} />;
}
function renderTemplate() {
return (
<ErrorBoundary catch={(err) => <div>Error: {err.stack}</div>}>
<MyAsyncComponent />
</ErrorBoundary>
);
}
// If MyAsyncComponent throws an error, it will render <div>Error: ...</div>
const html = await renderTemplate();
Error boundaries will only work for errors thrown inside async components, for sync components you must use try/catch.
function MySyncComponent() {
try {
const data = database.query(); // this may throw an error
return <User name={data.username} />;
} catch (err) {
return <div>Error: {err.stack}</div>;
}
}
Error boundaries outside suspense components will only catch errors thrown by the fallback
component. You must use the Suspense's catch property to handle errors thrown by its
children components.
function renderTemplate(rid: number) {
return (
<ErrorBoundary catch={<div>fallback error</div>}>
<Suspense
rid={rid}
fallback={<MyAsyncFallback />}
catch={<div>Children error</div>}
>
<MyAsyncComponent />
</Suspense>
</ErrorBoundary>
);
}
const html = renderToStream(renderTemplate);
The above example would render <div>Children error</div> if MyAsyncComponent throws an
error, or <div>fallback error</div> if MyAsyncFallback throws an error. If both throws
an error, the first error will be changed to the second error as soon as the children
error is thrown.
[!NOTE]
Until #14729 gets implemented, you need to manually castJSX.Elementinto strings if you are sure there is no inner async components in your component tree.
JSX elements are mostly strings everywhere. However, as the nature of this package, once a children element is a async component, the entire upper tree will also be async. Unless you are sure that no other component in your entire codebase is async, you should always handle both string and promise cases.
// It may or may not have inner async components.
const html = <Layout />;
if (html instanceof Promise) {
// I'm a promise, I should be awaited
console.log(await html);
} else {
// I'm a string, I can be used as is
console.log(html);
}
context API?We choose to not provide a context API. Here the reasons why:
This library only outputs strings (or Promises that resolve to strings), we don't manage
lifecycle or state. So the main selling point to having a context API is to avoid
prop drilling.
A context Api would need to use a request identifier (internally called rid) to be safe
to access asynchronously. Take for example two requests that are being processed at the
same time, both of them use some async components. If we use a global context without
scoping it behind some sort of rid, the second request would override the context of the
first request. So for the first request, some part of the rendering (the non async part)
would use the correct context, but then the other section inside the async component would
use the context of the second request. This is bad.. Each component that uses context
would need to receive the rid as a prop. This will defeat the purpose of having a
context in the first place. The rid is needed to make the context async safe.
The only way to maintain data consistency across concurrent renders without attaching a
request locator (rid), is by using
ALS. However, this
approach introduces a lot of overhead and a significant performance penalty.
Our recommendation is to use props. If you want to avoid prop drilling, you can use a composition style of writing components. This is a common pattern in other JSX-based libraries, and it works well with this library too.
// Drills only the required properties.
app.get('/', (request, response) => (
<YourDoctype title="Home">
<YourLayout loggedIn={!!request.user} lang={request.headers['accept-language']}>
<YourNavbar user={request.user} />
<YourContent />
<YourSubMenu path={request.url} username={request.user?.name} />
</YourLayout>
</YourDoctype>
));
Is it possible to use this library using the old jsx and jsxFactory options in your
tsconfig.json file. This is not recommended, but it is possible.
{
"compilerOptions": {
"jsx": "react",
"jsxFactory": "Html.createElement",
"jsxFragmentFactory": "Html.Fragment"
}
}
If you choose this approach keep in mind that you will need to manually import the Html
namespace in every file you use JSX.
import { Html } from '@kitajs/html';
const Html = (
<div>
<h1>Hello, world!</h1>
<p>Welcome to the KitaJS HTML package.</p>
</div>
);
And also there is a light performance penalty when using this approach. It's minimal, but it's there.
Migrating from plain HTML to JSX can be a pain to convert it all manually, as you will find yourself hand placing quotes and closing void elements.
You can use Html To Jsx.
<!-- Hello world -->
<div class="awesome" style="border: 1px solid red">
<label for="name">Enter your name: </label>
<input type="text" id="name" />
</div>
<p>Enter your HTML here</p>
Results into:
<>
{/* Hello world */}
<div className="awesome" style={{ border: '1px solid red' }}>
<label htmlFor="name">Enter your name: </label>
<input type="text" id="name" />
</div>
<p>Enter your HTML here</p>
</>
The usage of htmx.org is super common with this project, this is why we also provide type definitions for all HTMX attributes.
You just need to add this triple slash directive to the top of your file:
/// <reference types="@kitajs/html/htmx.d.ts" />
const html = (
// Type checking and intellisense for all HTMX attributes
<div hx-get="/api" hx-trigger="click" hx-target="#target">
Click me!
</div>
);
Or you can use the type option in your tsconfig to import the types globally:
{
"compilerOptions": {
"types": ["@kitajs/html/htmx.d.ts"]
}
}
Alpinejs is commonly used with htmx.
You just need to add this triple slash directive to the top of your file:
/// <reference types="@kitajs/html/alpine.d.ts" />
const html = (
// Type checking and intellisense for all HTMX attributes
<div x-data="{ open: false }">...</div>
);
Or you can use the type option in your tsconfig to import the types globally:
{
"compilerOptions": {
"types": ["@kitajs/html/alpine.d.ts"]
}
}
This project supports the usage of Turbo Hotwire. We provide a separate export that you can use to provide type definitions for the elements and attributes used with Turbo Hotwire.
You just need to add this triple slash directive to the top of your file:
/// <reference types="@kitajs/html/hotwire-turbo.d.ts" />
const html = (
// Type checking and intellisense for all HTMX attributes
<turbo-frame id="messages">
<a href="/messages/expanded">Show all expanded messages in this frame.</a>
<form action="/messages">Show response from this form within this frame.</form>
</turbo-frame>
);
Or you can use the type option in your tsconfig to import the types globally:
{
"compilerOptions": {
"types": ["@kitajs/html/hotwire-turbo.d.ts"]
}
}
Often you will have a "template" html with doctype, things on the head, body and so on... Most users try to use them as a raw string and only use JSX for other components, but this is a not a good idea as you will have problems with it.
But you can always concatenate strings, like in this required use-case for <doctype>
export function Layout(props: Html.PropsWithChildren<{ head: string; title?: string }>) {
return (
<>
{'<!doctype html>'}
<html lang="en">
<head>
<meta charset="UTF-8" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
<title>{props.title || 'Hello World!'}</title>
{props.head}
</head>
<body>{props.children}</body>
</html>
</>
);
}
const html = (
<Layout
head={
<>
<link rel="stylesheet" href="/style.css" />
<script src="/script.js" />
</>
}
>
<div>Hello World</div>
</Layout>
);
JSX does not allow multiple root elements, but you can use a fragment to group multiple elements:
const html = (
<>
<div>1</div>
<div>2</div>
</>
);
Learn more about JSX syntax here!
All HTML elements and attributes should be supported.
Missing an element or attribute? Please create an issue or a PR to add it. It's easy to add.
tag tagThe <tag of=""> tag is a custom internal tag that allows you to render any runtime
selected tag you want. Possibly reasons to prefer this tag over extending types:
<tag of="asd" />
// <asd></asd>
<tag of="my-custom-KEBAB" />
// <my-custom-KEBAB></my-custom-KEBAB>
We do recommend using extending types instead, as it will give you intellisense and type checking.
Kita supports constructing class attributes conditionally, which is a common use case
for many applications.
<div class={['a', true && 'b', false && 'c', 'd']} />
// <div class="a b d"></div>
<div class={['class-a class-b', true && 'class-c']} />
// <div class="class-a class-b class-c"></div>
This behavior is pretty similar and inspired from clsx, but we do not support objects as input.
Just as exemplified above, you may also want to add custom properties to your elements.
You can do this by extending the JSX namespace.
declare global {
namespace JSX {
// Adds a new element called mathPower
interface IntrinsicElements {
mathPower: HtmlTag & {
// Changes properties to the math-power element
['my-exponential']: number;
// this property becomes the <>{children}</> type
children: number;
};
}
// Adds hxBoost property to all elements native elements (those who extends HtmlTag)
interface HtmlTag {
['hx-boost']: boolean;
// TIP: We already provide HTMX types, check them out!
}
}
}
const element = (
<mathPower my-exponential={2} hx-boost>
{3}
</mathPower>
);
// Becomes <math-power my-exponential="2" hx-boost>3</math-power>
We also provide a way to allow any tag/attribute combination, altough we do not recommend using it.
Just add this triple slash directive to the top of your file:
/// <reference types="@kitajs/html/all-types.d.ts" />
This package is just a string builder on steroids, as you can see how this works. This means that most way to isolate performance differences is to micro benchmark.
The below benchmark compares this package with other popular HTML builders, like React, Typed Html, Common Tags and GHtml.
You can run this yourself by running pnpm bench.
[!NOTE]
This benchmark aims to represent real world usage, any tagged template library (like ghtml) will outperform any JSX library (like this one) when rendering a entire template within a singlehtml'<div>...</div>'call.
cpu: 13th Gen Intel(R) Core(TM) i5-13600K
runtime: node v20.11.0 (x64-linux)
benchmark time (avg) (min … max) p75 p99 p999
--------------------------------------------------- -----------------------------
• Many Components (31.4kb)
--------------------------------------------------- -----------------------------
KitaJS/Html 98'860 ns/iter (76'287 ns … 448 µs) 97'481 ns 238 µs 410 µs
Typed Html 738 µs/iter (635 µs … 1'398 µs) 779 µs 1'118 µs 1'398 µs
React 4'119 µs/iter (3'871 µs … 4'775 µs) 4'210 µs 4'755 µs 4'775 µs
Common Tags 2'815 µs/iter (2'565 µs … 3'461 µs) 2'905 µs 3'414 µs 3'461 µs
Ghtml 753 µs/iter (654 µs … 1'358 µs) 773 µs 1'080 µs 1'358 µs
summary for Many Components (31.4kb)
KitaJS/Html
7.46x faster than Typed Html
7.61x faster than Ghtml
28.47x faster than Common Tags
41.66x faster than React
• Many Props (7.4kb)
--------------------------------------------------- -----------------------------
KitaJS/Html 18'628 ns/iter (15'527 ns … 515 µs) 16'945 ns 60'084 ns 218 µs
Typed Html 76'473 ns/iter (65'986 ns … 509 µs) 70'509 ns 225 µs 379 µs
React 71'436 ns/iter (56'823 ns … 805 µs) 65'783 ns 272 µs 482 µs
Common Tags 43'080 ns/iter (36'634 ns … 594 µs) 39'846 ns 125 µs 357 µs
Ghtml 42'271 ns/iter (37'753 ns … 511 µs) 39'867 ns 101 µs 319 µs
summary for Many Props (7.4kb)
KitaJS/Html
2.27x faster than Ghtml
2.31x faster than Common Tags
3.83x faster than React
4.11x faster than Typed Html
• MdnHomepage (66.7Kb)
--------------------------------------------------- -----------------------------
KitaJS/Html 14'981 µs/iter (10'529 µs … 33'066 µs) 15'980 µs 33'066 µs 33'066 µs
Typed Html 28'667 µs/iter (25'501 µs … 36'842 µs) 30'385 µs 36'842 µs 36'842 µs
React 94'917 µs/iter (85'455 µs … 108 ms) 105 ms 108 ms 108 ms
Common Tags 39'634 µs/iter (37'625 µs … 40'880 µs) 40'517 µs 40'880 µs 40'880 µs
Ghtml 37'052 µs/iter (33'344 µs … 41'569 µs) 39'852 µs 41'569 µs 41'569 µs
summary for MdnHomepage (66.7Kb)
KitaJS/Html
1.91x faster than Typed Html
2.47x faster than Ghtml
2.65x faster than Common Tags
6.34x faster than React
This package just aims to be a drop in replacement syntax for JSX, and it works because you tell tsc to transpile JSX syntax to calls to our own JSX-runtime.
<ol start={2}>
{[1, 2].map((i) => (
<li>{i}</li>
))}
</ol>
Gets transpiled by tsc to plain javascript:
const runtime = require('@kitajs/html/jsx-runtime');
runtime.jsx('ol', {
start: 2,
children: [1, 2].map((i) => jsx('li', { children: i }))
});
Which, when called, returns this string:
'<ol start="2"><li>1</li><li>2</li></ol>';
Here is the table that explains how this library handles different types of children, describing the inputs and outputs.
[!IMPORTANT]
Arrays are simply concatenated with no separator.
| Input Type | Output Type |
|---|---|
<div>{"abc"}</div> | <div>abc</div> |
<div>{10}</div> | <div>10</div> |
<div>{NaN}</div> | <div>NaN</div> |
<div>{Infinity}</div> | <div>Infinity</div> |
<div>{true}</div> | <div>true</div> |
<div>{false}</div> | <div>false</div> |
<div>{null}</div> | <div></div> |
<div>{undefined}</div> | <div></div> |
<div>{[1, 2, 3]}</div> | <div>123</div> |
<div>{BigInt(123)}</div> | <div>123</div> |
This package emits HTML as a compact string, useful for over the wire environments. However, if your use case really needs the output HTML to be pretty printed, you can use an external JS library to do so, like html-prettify.
import prettify from 'html-prettify';
const html = (
<div>
<div>1</div>
<div>2</div>
</div>
);
console.log(html);
// <div><div>1</div><div>2</div></div>
console.log(prettify(html));
// <div>
// <div>1</div>
// <div>2</div>
// </div>
👉 There's an open PR to implement this feature natively, wanna work on it? Check this PR.
The @kitajs/html/register in favour of the react-jsx target @kitajs/html supports,
which automatically registers the JSX runtime globally.
Please update your tsconfig to use the new jsxImportSource option and remove all
references to '@kitajs/html/register' from your codebase.
{
"compilerOptions": {
+ "jsx": "react-jsx",
+ "jsxImportSource": "@kitajs/html",
- "jsx": "react",
- "jsxFactory": "Html.createElement",
- "jsxFragmentFactory": "Html.Fragment",
"plugins": [{ "name": "@kitajs/ts-html-plugin" }],
}
}
You can also remove all references to import { Html } from '@kitajs/html' from your
codebase.
- import { Html } from '@kitajs/html';
Importing type extensions like import '@kitajs/html/htmx' and
import '@kitajs/html/alpine' have been deprecated and will be removed in the next major
version.
Please change the way you import them to either use /// <reference types="..." />
triple slash directive
or the types option in your tsconfig.
- import '@kitajs/html/htmx';
+ /// <reference types="@kitajs/html/htmx" />
Or add them in the types option present in your tsconfig:
{
"compilerOptions": {
+ "types": ["@kitajs/html/htmx"]
}
}
This repository was initially forked from typed-html and modified to add some features and increase performance.
Initial credits to nicojs and contributors for the amazing work.
Licensed under the Apache License, Version 2.0.
FAQs
Fast and type safe HTML templates using TypeScript.
We found that @kitajs/html demonstrated a healthy version release cadence and project activity because the last version was released less than a year ago. It has 0 open source maintainers collaborating on the project.
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