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1.2.0 • Public • Published


xatto is View Layer Library based on Function and Context using VirtualDOM.
This is developed by forking from jorgebucaran/superfine.

Getting Started

Note: The example in this document assumes that you are using a JavaScript compiler such as Babel or TypeScript, a JSX (TSX) transpiler, and a module bundle such as Parcel, Webpack.

The main APIs of xatto are two.
The first one is xatto.x. It returns a new virtual DOM node tree.
The other is xatto.atto. It returns a function that mount (or update) a component in the specified DOM element. (mutate function)

example: A counter that can be incremented or decremented.

import { x, atto } from "xatto"
const down = context => ({ count: context.count - 1 })
const up = context => ({ count: context.count + 1 })
const Component = (props, children, context) => (
    <button onclick={down}>-</button>
    <button onclick={up}>+</button>
atto(Component, document.getElementById("app"))({
  count: 10


xatto is available as a package on npm.

npm install xatto
import { x, atto } from "xatto"

It is also available on a CDN.

<script src=""></script>
  var x = window.xatto.x;
  var atto = window.xatto.atto;
  // ...


git clone project
cd project
npm install
npm run serve



A context is a JavaScript object that describes a component.
It consists of dynamic data that moves within a component during execution.
To change the context you need to use the mutate function (or event handler in the components).

Mutate function

It is a function returned by xatto.atto.

Passing the context mount the component specified by xatto.atto on the specified container together.
From the second time on, it update.


The component returns the specification in the form of a plain JavaScript object called virtual DOM, and xatto is updates the actual DOM accordingly.
Each time the context changes the component is invoked so you can specify the appearance of the DOM based on the new context.

The context can be referenced in the third arguments.

import { x, atto } from "xatto"
const Component = (props, children, context) => (
atto(Component, document.getElementById("app"))({
  name: "foo"

Fragments supported

const Component = (props, children) => (

Sliced context and fill

The child component can treat a part of the context as if it were the root context by using <Context slice="path"> in the parent component.

Also, the fill attribute can specify a value to use if part of the sliced context is undefined.

import { x, atto, Context } from "xatto"
const Parent = (props, children, context) => (
      <li><Context slice="children.0"><Child /></Context></li>
      <li><Context slice="children.1" fill={{ name: "baz" }}><Child /></Context></li>
const Child = (props, children, context) => (
atto(Parent, document.getElementById("app"))({
  name: "foo",
  children: [
      name: "bar"


Event handlers are wrapped by xatto.
Usually, the event object passed in the first argument is the fourth argument.
The return value is passed to the mutate function.

Event handler arguments:

  1. context
  2. { ...extra, ...detail }
  3. props
  4. event

Lifecycle Events

Lifecycle events can be used to be notified when an element managed by the virtual DOM is created, updated, or deleted.
It can be used for animation, data fetching, third party library wrapping, resource cleanup, etc.


This event occurs after an element is created and attached to the DOM.


This event will occur each time you update an element's attributes.


This event occurs before an element is dettached from the DOM.
detail.done is passed a function to detach the element.


This event occurs just before an element is dettached from the DOM.


This event occurs just before each life cycle event occurs.
detail.type is passed the life cycle event name.


The key helps to identify the node each time xatto update the DOM.
This allows you to rearrange the elements to a new position if you change the position.

The key must be unique among sibling nodes.

Polyfill which may be needed


xatto is MIT licensed. See LICENSE.

Other examples

The counters.

import { x, atto, Context } from "xatto"
const down = context => ({ count: context.count - 1 })
const up = context => ({ count: context.count + 1 })
const Counter = (props, children, context) => (
    <button onclick={down}>-</button>
    <button onclick={up}>+</button>
const add = context => ({
  counters: context.counters.concat({count: 0})
const cut = context => ({
  counters: context.counters.slice(0, -1)
const Main = (props, children, context) => (
    <button onclick={add}>add</button>
    <button onclick={cut}>cut</button>
      .map((v, i) => (<Context slice={'counters.' + i}><Counter /></Context>))}
    <pre>{JSON.stringify(context, null, '  ')}</pre>
atto(Main, document.getElementById("app"))({
  counters: [
    { count: 0 },
    { count: 10 }


npm i xatto

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