snabbdom/README-zh_CN.md

A virtual DOM library with focus on simplicity, modularity, powerful features and performance.

一个精简化、模块化、功能强大、性能卓越的虚拟 DOM 库。

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Thanks to Browserstack for providing access to their great cross-browser testing tools.

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介绍

Virtual DOM is awesome. It allows us to express our application's view as a function of its state. But existing solutions were way way too bloated, too slow, lacked features, had an API biased towards OOP and/or lacked features I needed.

Snabbdom consists of an extremely simple, performant and extensible core that is only ≈ 200 SLOC. It offers a modular architecture with rich functionality for extensions through custom modules. To keep the core simple, all non-essential functionality is delegated to modules.

You can mold Snabbdom into whatever you desire! Pick, choose and customize the functionality you want. Alternatively you can just use the default extensions and get a virtual DOM library with high performance, small size and all the features listed below.

虚拟DOM非常有趣，他允许我们以对象的形式来表达程序视图，但现有的解决方式基本都过于臃肿、性能不佳、功能缺乏、API偏向于OOP或者缺少一些我所需要的功能。

Snabbdom 则极其简单、高效并且可拓展，同时核心代码 ≈ 200行。我们提供了一个具有丰富功能同时支持自定义拓展的模块化结构。为了使核心代码更简洁，所有非必要的功能都将模块化引入。

你可以将 Snabbdom 改造成任何你想要的样子！选择或自定义任何你需要的功能。或者使用默认配置，便能获得一个高性能、体积小、拥有下列所有特性的虚拟 DOM 库。

特性

• 主要特点
  • About 200 SLOC – you could easily read through the entire core and fully understand how it works.
  • 200行 - 你可以通过简单地阅读所有核心代码来充分理解其工作原理。
  • Extendable through modules.
  • 通过模块化实现可拓展。
  • A rich set of hooks available, both per vnode and globally for modules, to hook into any part of the diff and patch process.
  • 对于vnode和全局模块都提供了 hook，你可以在 patch 过程或者其他地方调用 hook。
  • Splendid performance. Snabbdom is among the fastest virtual DOM libraries.
  • 性能卓越：Snabbdom 是目前最高效的虚拟DOM库之一。
  • Patch function with a function signature equivalent to a reduce/scan function. Allows for easier integration with a FRP library.
  • Patch 函数有一个相当于 reduce/scan 函数的函数签名，这将更容易集成其他函数式库。
• 模块特点
  • h function for easily creating virtual DOM nodes.
  • 函数h： 通过该创建虚拟 DOM nodes
  • SVG just works with the h helper.
  • SVG 需要与 h 函数结合使用
  • Features for doing complex CSS animations.
  • 支持复杂的CSS动画实现
  • Powerful event listener functionality.
  • 提供强大的事件监听功能
  • Thunks to optimize the diff and patch process even further.
  • 通过 Thunks 进一步优化 diff 和 patch 过程
  • JSX support, including TypeScript types
  • 支持 JSX 及 Typrscript
• 第三方功能
  • Server-side HTML output provided by snabbdom-to-html.
  • snabbdom-to-html 提供服务端渲染功能
  • Compact virtual DOM creation with snabbdom-helpers.
  • snabbdom-helpers 精简版虚拟DOM创建
  • Template string support using snabby.
  • snabby 提供 HTML 模板字符串支持
  • Virtual DOM assertion with snabbdom-looks-like
  • snabbdom-looks-like 提供虚拟 DOM 断言

示例

import {
  init,
  classModule,
  propsModule,
  styleModule,
  eventListenersModule,
  h,
} from "snabbdom";

const patch = init([
  // 通过传入模块初始化 patch 函数
  classModule, // 开启 classes 功能
  propsModule, // 支持传入 props
  styleModule, // 支持内联样式同时支持动画
  eventListenersModule, // 添加事件监听
]);

const container = document.getElementById("container");

const vnode = h("div#container.two.classes", { on: { click: someFn } }, [
  h("span", { style: { fontWeight: "bold" } }, "This is bold"),
  " and this is just normal text",
  h("a", { props: { href: "/foo" } }, "I'll take you places!"),
]);
// 传入一个空的元素节点 - 将产生副作用（修改该节点）
patch(container, vnode);

const newVnode = h(
  "div#container.two.classes",
  { on: { click: anotherEventHandler } },
  [
    h(
      "span",
      { style: { fontWeight: "normal", fontStyle: "italic" } },
      "This is now italic type"
    ),
    " and this is still just normal text",
    h("a", { props: { href: "/bar" } }, "I'll take you places!"),
  ]
);
// 再次调用 `patch` 
patch(vnode, newVnode); // 将旧节点更新为新节点

更多示例

• Animated reordering of elements
• Hero transitions
• SVG Carousel

---

仙人指路

• 核心功能
  • init
  • patch
    • 卸载
  • h
  • fragment (experimental)
  • tovnode
  • Hooks
    • Overview
    • Usage
    • The init hook
    • The insert hook
    • The remove hook
    • The destroy hook
  • Creating modules
• Modules documentation
  • The class module
  • The props module
  • The attributes module
  • The dataset module
  • The style module
    • Custom properties (CSS variables)
    • Delayed properties
    • Set properties on remove
    • Set properties on destroy
  • The eventlisteners module
• SVG
  • Classes in SVG Elements
• Thunks
• JSX
  • TypeScript
  • Babel
• Virtual Node
  • sel : String
  • data : Object
  • children : Array
  • text : string
  • elm : Element
  • key : string | number
• Structuring applications
• Common errors
• Opportunity for community feedback

核心功能

The core of Snabbdom provides only the most essential functionality. It is designed to be as simple as possible while still being fast and extendable.

Snabbdom 仅提供通用的核心部分，这种设计保证了核心代码的纯粹，与此同时又使其更快并且对可拓展性提供更好的支持。

init

The core exposes only one single function init. This init takes a list of modules and returns a patch function that uses the specified set of modules.

核心功能暴露一个 init 函数，这个 init 函数接收一个包含模块的数组并返回一个具有指定功能的 patch 函数 。

import { init, classModule, styleModule } from "snabbdom";

const patch = init([classModule, styleModule]);

patch

The patch function returned by init takes two arguments. The first is a DOM element or a vnode representing the current view. The second is a vnode representing the new, updated view.

通过调用 init 函数返回的 patch 函数具有两个参数：

1. 一个 DOM element 或者 一个表示当前视图的 vnode 元素
2. 一个表示新的、需要更新的 vnode 元素

If a DOM element with a parent is passed, newVnode will be turned into a DOM node, and the passed element will be replaced by the created DOM node. If an old vnode is passed, Snabbdom will efficiently modify it to match the description in the new vnode.

如果第一个参数传入一个包含父节点的 DOM element，那么 newVnode 将转换为一个 DOM node 并替换传入的元素。如果第一个参数传入的是一个 vnode 则根据新的 vnode 相关描述进行修改。

Any old vnode passed must be the resulting vnode from a previous call to patch. This is necessary since Snabbdom stores information in the vnode. This makes it possible to implement a simpler and more performant architecture. This also avoids the creation of a new old vnode tree.

所有传入的 oldvnode 都必须被传入过 patch 函数， 因为 Snabbdom 将信息存储在 vnode 中， 这避免了重复创建新的 vnode 树。

patch(oldVnode, newVnode);

卸载

While there is no API specifically for removing a VNode tree from its mount point element, one way of almost achieving this is providing a comment VNode as the second argument to patch, such as:

虽然没有专门为移除 vnode 树中的节点提供 API，但是依然可以通过给 patch 函数传入一个 HTML注释的 vnode 作为第二个参数来实现相同的效果，如：

patch(
  oldVnode,
  h("!", {
    hooks: {
      post: () => {
        /* patch complete */
      },
    },
  })
);

Of course, then there is still a single comment node at the mount point.

当然，那里依然会有一个注释节点被挂载。

h

It is recommended that you use h to create vnodes. It accepts a tag/selector as a string, an optional data object and an optional string or array of children.

我们推荐您使用函数 h 来创建 vnodes，这个函数接收一个字符串类型的 tag/selector、一个数据对象（可选）、一个子节点数组或字符串（可选）。

import { h } from "snabbdom";

const vnode = h("div", { style: { color: "#000" } }, [
  h("h1", "Headline"),
  h("p", "A paragraph"),
]);

fragment (试验性)

Caution: This feature is currently experimental and must be opted in. Its API may be changed without an major version bump.

警告：此功能目前处于试验阶段必须手动开启，并且这个API可能会在未来小版本更新中被修改。

const patch = init(modules, undefined, {
  experimental: {
    fragments: true,
  },
});

Creates a virtual node that will be converted to a document fragment containing the given children.

创建一个虚拟节点并转换为一个包含子元素的 document fragment（文档碎片）。

import { fragment, h } from "snabbdom";

const vnode = fragment(["I am", h("span", [" a", " fragment"])]);

tovnode

Converts a DOM node into a virtual node. Especially good for patching over an pre-existing, server-side generated content.

将一个 DOM 节点转换为一个虚拟节点，这非常有利于服务端渲染。

import {
  init,
  classModule,
  propsModule,
  styleModule,
  eventListenersModule,
  h,
  toVNode,
} from "snabbdom";

const patch = init([
  // Init patch function with chosen modules
  classModule, // makes it easy to toggle classes
  propsModule, // for setting properties on DOM elements
  styleModule, // handles styling on elements with support for animations
  eventListenersModule, // attaches event listeners
]);

const newVNode = h("div", { style: { color: "#000" } }, [
  h("h1", "Headline"),
  h("p", "A paragraph"),
]);

patch(toVNode(document.querySelector(".container")), newVNode);

Hooks

Hooks are a way to hook into the lifecycle of DOM nodes. Snabbdom offers a rich selection of hooks. Hooks are used both by modules to extend Snabbdom, and in normal code for executing arbitrary code at desired points in the life of a virtual node.

Snabbdom 提供了一系列丰富的生命周期函数，这些生命周期函数适用于拓展 Snabbdom 模块或者在 virtual node 生命周期中的任意节点执行任意代码。

概览

名称	触发节点	回调参数
pre	patch 开始执行	none
init	vnode 被添加	vnode
create	一个基于 vnode 的 DOM element 被创建	emptyVnode, vnode
insert	element 被插入到 DOM	vnode
prepatch	element 即将 patch	oldVnode, vnode
update	element 已更新	oldVnode, vnode
postpatch	element 已被 patch	oldVnode, vnode
destroy	element 被直接或间接得移除	vnode
remove	element 已从 DOM 中移除	vnode, removeCallback
post	已完成 patch 过程	none

The following hooks are available for modules: pre, create, update, destroy, remove, post.

适用于模块：pre, create,update, destroy, remove, post。

The following hooks are available in the hook property of individual elements: init, create, insert, prepatch, update, postpatch, destroy, remove.

适用于单个元素：init, create, insert, prepatch, update,postpatch, destroy, remove。

使用

To use hooks, pass them as an object to hook field of the data object argument.

使用 hooks 时， 请将所需要的 hook 以对象的形式（key 为对应 hook 字段）作为参数传入。

h("div.row", {
  key: movie.rank,
  hook: {
    insert: (vnode) => {
      movie.elmHeight = vnode.elm.offsetHeight;
    },
  },
});

init

This hook is invoked during the patch process when a new virtual node has been found. The hook is called before Snabbdom has processed the node in any way. I.e., before it has created a DOM node based on the vnode.

这个钩子函数会在新的 vnode 创建后被调用，在 Snabbdom 以任何方式处理该节点前被调用，即：在 create 之前被调用。

insert

This hook is invoked once the DOM element for a vnode has been inserted into the document and the rest of the patch cycle is done. This means that you can do DOM measurements (like using getBoundingClientRect in this hook safely, knowing that no elements will be changed afterwards that could affect the position of the inserted elements.

当基于 vnode 的 DOM element 被插入到文档后并且 patch 其余过程完成后调用，这意味着你可以在这个 hook 中更可靠地计算元素位置坐标信息（如：getBoundingClientRect），这种操作不会影响任何被插入元素的位置。

remove

Allows you to hook into the removal of an element. The hook is called once a vnode is to be removed from the DOM. The handling function receives both the vnode and a callback. You can control and delay the removal with the callback. The callback should be invoked once the hook is done doing its business, and the element will only be removed once all remove hooks have invoked their callback.

一旦从 DOM 中移除了 vnode 就会调用该函数，函数需要传入 vnode 和 回调函数 作为参数，你可以通过回调来控制或延迟移除，这个回调函数将会在 hook 执行完成后调用，需要注意的是只有当所有 remove hooks 执行完所有回调之后元素才会被一次性删除。

The hook is only triggered when an element is to be removed from its parent – not if it is the child of an element that is removed. For that, see the destroy hook.

这个 hook 只有在当前元素从父级中删除才会触发，从元素中移除子元素则不会触发。

destroy

This hook is invoked on a virtual node when its DOM element is removed from the DOM or if its parent is being removed from the DOM.

当虚拟节点的DOM元素从DOM中移除或者元素父级从DOM中移除时将触发该 hook。

To see the difference between this hook and the remove hook, consider an example.

要知道这个 hook 和 remove hook 的区别，先看看这个示例

const vnode1 = h("section", [
  h(
    "div",
    {
      hook: {
        remove: (vnode, cb) => {
          console.log(vnode);
          cb();
        }
      }
    },
    [h("span", "Hello")]
  )
]);
const vnode2 = h("section", []);
patch(container, vnode1);
patch(vnode1, vnode2);

Here destroy is triggered for both the inner div element and the span element it contains. remove, on the other hand, is only triggered on the div element because it is the only element being detached from its parent.

这里内部 div 元素及其包含的 span 元素都会触发 destroy， 另一方面，remove 则只会在 div 上触发，因为他是唯一一个脱离父级的元素。

You can, for instance, use remove to trigger an animation when an element is being removed and use the destroy hook to additionally animate the disappearance of the removed element's children.

比如，你可以使用 remove 在元素被移除时触发动画，再使用 destroy 为子元素添加消失动画。

创建模块

Modules works by registering global listeners for hooks. A module is simply a dictionary mapping hook names to functions.

模块是通过全局注册 hook 监听实现，一个模块就相当于是 hook 的映射。

const myModule = {
  create: function (oldVnode, vnode) {
    // invoked whenever a new virtual node is created
  },
  update: function (oldVnode, vnode) {
    // invoked whenever a virtual node is updated
  },
};

With this mechanism you can easily augment the behaviour of Snabbdom. For demonstration, take a look at the implementations of the default modules.

通过这种方法你可以很容易得增加 Snabbdom 的行为。为了更好的展示，请查看默认模块的实现。

模块文档

This describes the core modules. All modules are optional. JSX examples assume you're using the jsx pragma provided by this library.

本章节将描述核心模块，所有模块都是可选的，关于 JSX 示例我们将假定你使用的 jsx pragma 与本库一致。

模块 class

The class module provides an easy way to dynamically toggle classes on elements. It expects an object in the class data property. The object should map class names to booleans that indicates whether or not the class should stay or go on the vnode.

class 模块提供了一种简单的方式来动态配置元素的 class 属性，这个模块值为一个对象形式的 class 数据，对象中类名需要映射为布尔值，以此来表示该类名是否应该出现在节点上。

h("a", { class: { active: true, selected: false } }, "Toggle");

In JSX, you can use class like this:

在 JSX 中，你可以这样使用 class：

<div class={{ foo: true, bar: true }} />
// Renders as: <div class="foo bar"></div>

模块 props

Allows you to set properties on DOM elements.

该模块允许你设置 DOM 元素的属性。

h("a", { props: { href: "/foo" } }, "Go to Foo");

In JSX, you can use props like this:

在 JSX 中，你可以这样使用 props：

<input props={{ name: "foo" }} />
// Renders as: <input name="foo" /> with input.name === "foo"

Properties can only be set. Not removed. Even though browsers allow addition and deletion of custom properties, deletion will not be attempted by this module. This makes sense, because native DOM properties cannot be removed. And if you are using custom properties for storing values or referencing objects on the DOM, then please consider using data-* attributes instead. Perhaps via the dataset module.

属性只能被设置不能被移除，即使浏览器允许自定义添加或删除属性，该模块也不会尝试删除。这是因为原生 DOM 的属性也同样不支持被移除，如果你是通过自定义属性来存储信息或者引用对象，那么请考虑使用 data-* attributes 代替，为此我们提供了 dataset 模块。

模块 attributes

Same as props, but set attributes instead of properties on DOM elements.

与 props 相同，但是是使用 attr 替代 prop。

h("a", { attrs: { href: "/foo" } }, "Go to Foo");

In JSX, you can use attrs like this:

在 JSX 中，你可以这样使用 attrs：

<div attrs={{ "aria-label": "I'm a div" }} />
// Renders as: <div aria-label="I'm a div"></div>

Attributes are added and updated using setAttribute. In case of an attribute that had been previously added/set and is no longer present in the attrs object, it is removed from the DOM element's attribute list using removeAttribute.

Attr 通过 setAttribute 实现添加及更新操作，对于已经添加过的属性，如果该属性不存在于 attrs 对象中那么将通过 removeAttribute 将其从 DOM 元素属性列表中移除。

In the case of boolean attributes (e.g. disabled, hidden, selected ...), the meaning doesn't depend on the attribute value (true or false) but depends instead on the presence/absence of the attribute itself in the DOM element. Those attributes are handled differently by the module: if a boolean attribute is set to a falsy value (0, -0, null, false,NaN, undefined, or the empty string ("")), then the attribute will be removed from the attribute list of the DOM element.

对于布尔值属性（如：disabled, hidden,selected ...），这一类属性并不依赖于 Attr 的值(true 或 false)，而是取决于 DOM 元素本身是否存在该属性。模块对于这类属性的处理方式有些许不同，当一个布尔值属性被赋为 假值 (0, -0, null, false,NaN, undefined, or the empty string(""))，那么该属性同样会直接从 DOM 元素的属性列表中移除。

模块 dataset

Allows you to set custom data attributes (data-*) on DOM elements. These can then be accessed with the HTMLElement.dataset property.

允许你在 DOM 元素上设置自定义 data 属性，然后通过 HTMLElement.dataset 来访问这些属性。

h("button", { dataset: { action: "reset" } }, "Reset");

In JSX, you can use dataset like this:

在 JSX 中，你可以这样使用 dataset：

<div dataset={{ foo: "bar" }} />
// Renders as: <div data-foo="bar"></div>

模块 style

The style module is for making your HTML look slick and animate smoothly. At its core it allows you to set CSS properties on elements.

style 模块用于让动画更加平滑，它的核心是允许你再元素上设置 CSS 属性。

h(
  "span",
  {
    style: {
      border: "1px solid #bada55",
      color: "#c0ffee",
      fontWeight: "bold",
    },
  },
  "Say my name, and every colour illuminates"
);

In JSX, you can use style like this:

在 JSX 中，你可以这样使用 style：

<div
  style={{
    border: "1px solid #bada55",
    color: "#c0ffee",
    fontWeight: "bold",
  }}
/>
// Renders as: <div style="border: 1px solid #bada55; color: #c0ffee; font-weight: bold"></div>

Note that the style module does not remove style attributes if they are removed as properties from the style object. To remove a style, you should instead set it to the empty string.

h(
  "div",
  {
    style: { position: shouldFollow ? "fixed" : "" },
  },
  "I, I follow, I follow you"
);

自定义属性(CSS变量)

CSS custom properties (aka CSS variables) are supported, they must be prefixed with --

已支持 CSS 自定义属性（又称 CSS 变量或者级联变量），属性名需要以 -- 为前缀。

h(
  "div",
  {
    style: { "--warnColor": "yellow" },
  },
  "Warning"
);

属性 delayed

You can specify properties as being delayed. Whenever these properties change, the change is not applied until after the next frame.

你可以指定延迟属性，每当这些属性变动时需要到下一帧之后才会应用更改。

h(
  "span",
  {
    style: {
      opacity: "0",
      transition: "opacity 1s",
      delayed: { opacity: "1" },
    },
  },
  "Imma fade right in!"
);

This makes it easy to declaratively animate the entry of elements.

这使得声明方式设置元素入场动画变得容易。

The all value of transition-property is not supported.

不支持 transition-property 的所有值。

属性 remove

Styles set in the remove property will take effect once the element is about to be removed from the DOM. The applied styles should be animated with CSS transitions. Only once all the styles are done animating will the element be removed from the DOM.

设置到 remove 中的样式属性将会在元素即将从 DOM 中移除时生效，应用的样式应该通过 CSS transition 设置，只有当所有动画样式完成后元素才会从 DOM 中移除。

h(
  "span",
  {
    style: {
      opacity: "1",
      transition: "opacity 1s",
      remove: { opacity: "0" },
    },
  },
  "It's better to fade out than to burn away"
);

This makes it easy to declaratively animate the removal of elements.

这使得声明方式设置元素出场动画变得容易。

The all value of transition-property is not supported.

不支持 transition-property 的所有值。

属性 destroy

h(
  "span",
  {
    style: {
      opacity: "1",
      transition: "opacity 1s",
      destroy: { opacity: "0" },
    },
  },
  "It's better to fade out than to burn away"
);

The all value of transition-property is not supported.

不支持 transition-property 的所有值。

模块 eventlisteners

The event listeners module gives powerful capabilities for attaching event listeners.

eventlisteners 模块提供了一个功能强大的事件监听器。

You can attach a function to an event on a vnode by supplying an object at on with a property corresponding to the name of the event you want to listen to. The function will be called when the event happens and will be passed the event object that belongs to it.

你可以通过给 on 提供一个对象以此来将事件函数绑定到 vnode上，对象包含你要监听的事件名称和对应函数，函数将会在事件发生时触发并传递相应的事件对象。

function clickHandler(ev) {
  console.log("got clicked");
}
h("div", { on: { click: clickHandler } });

In JSX, you can use on like this:

在 JSX 中，你可以这样使用 on：

<div on={{ click: clickHandler }} />

Snabbdom allows swapping event handlers between renders. This happens without actually touching the event handlers attached to the DOM.

Snabbdom 允许在 renders 之间交换事件处理，这种情况发生时并没有实际触发 DOM 的事件处理。

Note, however, that you should be careful when sharing event handlers between vnodes, because of the technique this module uses to avoid re-binding event handlers to the DOM. (And in general, sharing data between vnodes is not guaranteed to work, because modules are allowed to mutate the given data).

In particular, you should not do something like this:

// Does not work
const sharedHandler = {
  change: function (e) {
    console.log("you chose: " + e.target.value);
  },
};
h("div", [
  h("input", {
    props: { type: "radio", name: "test", value: "0" },
    on: sharedHandler,
  }),
  h("input", {
    props: { type: "radio", name: "test", value: "1" },
    on: sharedHandler,
  }),
  h("input", {
    props: { type: "radio", name: "test", value: "2" },
    on: sharedHandler,
  }),
]);

For many such cases, you can use array-based handlers instead (described above). Alternatively, simply make sure each node is passed unique on values:

// Works
const sharedHandler = function (e) {
  console.log("you chose: " + e.target.value);
};
h("div", [
  h("input", {
    props: { type: "radio", name: "test", value: "0" },
    on: { change: sharedHandler },
  }),
  h("input", {
    props: { type: "radio", name: "test", value: "1" },
    on: { change: sharedHandler },
  }),
  h("input", {
    props: { type: "radio", name: "test", value: "2" },
    on: { change: sharedHandler },
  }),
]);

SVG

SVG just works when using the h function for creating virtual nodes. SVG elements are automatically created with the appropriate namespaces.

const vnode = h("div", [
  h("svg", { attrs: { width: 100, height: 100 } }, [
    h("circle", {
      attrs: {
        cx: 50,
        cy: 50,
        r: 40,
        stroke: "green",
        "stroke-width": 4,
        fill: "yellow",
      },
    }),
  ]),
]);

See also the SVG example and the SVG Carousel example.

Classes in SVG Elements

Certain browsers (like IE <=11) do not support classList property in SVG elements. Because the class module internally uses classList, it will not work in this case unless you use a classList polyfill. (If you don't want to use a polyfill, you can use the class attribute with the attributes module).

Thunks

The thunk function takes a selector, a key for identifying a thunk, a function that returns a vnode and a variable amount of state parameters. If invoked, the render function will receive the state arguments.

thunk(selector, key, renderFn, [stateArguments])

The renderFn is invoked only if the renderFn is changed or [stateArguments] array length or it's elements are changed.

The key is optional. It should be supplied when the selector is not unique among the thunks siblings. This ensures that the thunk is always matched correctly when diffing.

Thunks are an optimization strategy that can be used when one is dealing with immutable data.

Consider a simple function for creating a virtual node based on a number.

function numberView(n) {
  return h("div", "Number is: " + n);
}

The view depends only on n. This means that if n is unchanged, then creating the virtual DOM node and patching it against the old vnode is wasteful. To avoid the overhead we can use the thunk helper function.

function render(state) {
  return thunk("num", numberView, [state.number]);
}

Instead of actually invoking the numberView function this will only place a dummy vnode in the virtual tree. When Snabbdom patches this dummy vnode against a previous vnode, it will compare the value of n. If n is unchanged it will simply reuse the old vnode. This avoids recreating the number view and the diff process altogether.

The view function here is only an example. In practice thunks are only relevant if you are rendering a complicated view that takes significant computational time to generate.

JSX

TypeScript

Add the following options to your tsconfig.json:

{
  "compilerOptions": {
    "jsx": "react",
    "jsxFactory": "jsx"
  }
}

Then make sure that you use the .tsx file extension and import the jsx function at the top of the file:

import { jsx, VNode } from "snabbdom";

const node: VNode = (
  <div>
    <span>I was created with JSX</span>
  </div>
);

Babel

Add the following options to your babel configuration:

{
  "plugins": [
    [
      "@babel/plugin-transform-react-jsx",
      {
        "pragma": "jsx"
      }
    ]
  ]
}

Then import the jsx function at the top of the file:

import { jsx } from "snabbdom";

const node = (
  <div>
    <span>I was created with JSX</span>
  </div>
);

Virtual Node

Properties

• sel
• data
• children
• text
• elm
• key

sel : String

The .sel property of a virtual node is the CSS selector passed to h() during creation. For example: h('div#container', {}, [...]) will create a a virtual node which has div#container as its .sel property.

data : Object

The .data property of a virtual node is the place to add information for modules to access and manipulate the real DOM element when it is created; Add styles, CSS classes, attributes, etc.

The data object is the (optional) second parameter to h()

For example h('div', {props: {className: 'container'}}, [...]) will produce a virtual node with

({
  props: {
    className: "container",
  },
});

as its .data object.

children : Array

The .children property of a virtual node is the third (optional) parameter to h() during creation. .children is simply an Array of virtual nodes that should be added as children of the parent DOM node upon creation.

For example h('div', {}, [ h('h1', {}, 'Hello, World') ]) will create a virtual node with

[
  {
    sel: "h1",
    data: {},
    children: undefined,
    text: "Hello, World",
    elm: Element,
    key: undefined,
  },
];

as its .children property.

text : string

The .text property is created when a virtual node is created with only a single child that possesses text and only requires document.createTextNode() to be used.

For example: h('h1', {}, 'Hello') will create a virtual node with Hello as its .text property.

elm : Element

The .elm property of a virtual node is a pointer to the real DOM node created by snabbdom. This property is very useful to do calculations in hooks as well as modules.

key : string | number

The .key property is created when a key is provided inside of your .data object. The .key property is used to keep pointers to DOM nodes that existed previously to avoid recreating them if it is unnecessary. This is very useful for things like list reordering. A key must be either a string or a number to allow for proper lookup as it is stored internally as a key/value pair inside of an object, where .key is the key and the value is the .elm property created.

If provided, the .key property must be unique among sibling elements.

For example: h('div', {key: 1}, []) will create a virtual node object with a .key property with the value of 1.

Structuring applications

Snabbdom is a low-level virtual DOM library. It is unopinionated with regards to how you should structure your application.

Here are some approaches to building applications with Snabbdom.

• functional-frontend-architecture – a repository containing several example applications that demonstrates an architecture that uses Snabbdom.
• Cycle.js – "A functional and reactive JavaScript framework for cleaner code" uses Snabbdom
• Vue.js use a fork of snabbdom.
• scheme-todomvc build redux-like architecture on top of snabbdom bindings.
• kaiju - Stateful components and observables on top of snabbdom
• Tweed – An Object Oriented approach to reactive interfaces.
• Cyclow - "A reactive frontend framework for JavaScript" uses Snabbdom
• Tung – A JavaScript library for rendering html. Tung helps to divide html and JavaScript development.
• sprotty - "A web-based diagramming framework" uses Snabbdom.
• Mark Text - "Realtime preview Markdown Editor" build on Snabbdom.
• puddles - "Tiny vdom app framework. Pure Redux. No boilerplate." - Built with ❤️ on Snabbdom.
• Backbone.VDOMView - A Backbone View with VirtualDOM capability via Snabbdom.
• Rosmaro Snabbdom starter - Building user interfaces with state machines and Snabbdom.
• Pureact - "65 lines implementation of React incl Redux and hooks with only one dependency - Snabbdom"
• Snabberb - A minimalistic Ruby framework using Opal and Snabbdom for building reactive views.
• WebCell - Web Components engine based on JSX & TypeScript

Be sure to share it if you're building an application in another way using Snabbdom.

Common errors

Uncaught NotFoundError: Failed to execute 'insertBefore' on 'Node':
    The node before which the new node is to be inserted is not a child of this node.

The reason for this error is reusing of vnodes between patches (see code example), snabbdom stores actual dom nodes inside the virtual dom nodes passed to it as performance improvement, so reusing nodes between patches is not supported.

const sharedNode = h("div", {}, "Selected");
const vnode1 = h("div", [
  h("div", {}, ["One"]),
  h("div", {}, ["Two"]),
  h("div", {}, [sharedNode]),
]);
const vnode2 = h("div", [
  h("div", {}, ["One"]),
  h("div", {}, [sharedNode]),
  h("div", {}, ["Three"]),
]);
patch(container, vnode1);
patch(vnode1, vnode2);

You can fix this issue by creating a shallow copy of the object (here with object spread syntax):

const vnode2 = h("div", [
  h("div", {}, ["One"]),
  h("div", {}, [{ ...sharedNode }]),
  h("div", {}, ["Three"]),
]);

Another solution would be to wrap shared vnodes in a factory function:

const sharedNode = () => h("div", {}, "Selected");
const vnode1 = h("div", [
  h("div", {}, ["One"]),
  h("div", {}, ["Two"]),
  h("div", {}, [sharedNode()]),
]);

Opportunity for community feedback

Pull requests that the community may care to provide feedback on should be merged after such opportunity of a few days was provided.