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https://github.com/webreflection/linkedom
A triple-linked lists based DOM implementation.
https://github.com/webreflection/linkedom
dom ssr web
Last synced: about 1 month ago
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A triple-linked lists based DOM implementation.
- Host: GitHub
- URL: https://github.com/webreflection/linkedom
- Owner: WebReflection
- License: isc
- Created: 2020-12-13T16:51:36.000Z (about 4 years ago)
- Default Branch: main
- Last Pushed: 2024-10-22T10:48:44.000Z (2 months ago)
- Last Synced: 2024-11-08T17:52:42.371Z (about 1 month ago)
- Topics: dom, ssr, web
- Language: HTML
- Homepage: https://webreflection.medium.com/linkedom-a-jsdom-alternative-53dd8f699311
- Size: 3.34 MB
- Stars: 1,690
- Watchers: 12
- Forks: 83
- Open Issues: 32
-
Metadata Files:
- Readme: README.md
- License: LICENSE
Awesome Lists containing this project
README
# 🔗 linkedom
[](https://www.npmjs.com/package/linkedom) [](https://travis-ci.com/WebReflection/linkedom) [](https://coveralls.io/github/WebReflection/linkedom?branch=main)
**Social Media Photo by [JJ Ying](https://unsplash.com/@jjying) on [Unsplash](https://unsplash.com/)**
### This is not a crawler!
LinkeDOM is a [triple-linked list](#data-structure) based DOM-like namespace, for DOM-less environments, with the following goals:
* **avoid** maximum callstack/recursion or **crashes**, even under heaviest conditions.
* guarantee **linear performance** from small to big documents.
* be **close to the** current **DOM standard**, but [not too close](https://github.com/WebReflection/linkedom#faq).
```js
import {DOMParser, parseHTML} from 'linkedom';
// Standard way: text/html, text/xml, image/svg+xml, etc...
// const document = (new DOMParser).parseFromString(html, 'text/html');
// Simplified way for HTML
const {
// note, these are *not* globals
window, document, customElements,
HTMLElement,
Event, CustomEvent
// other exports ..
} = parseHTML(`
Hello SSR
Submit
`);
// builtin extends compatible too 👍
customElements.define('custom-element', class extends HTMLElement {
connectedCallback() {
console.log('it works 🥳');
}
});
document.body.appendChild(
document.createElement('custom-element')
);
document.toString();
// the SSR ready document
document.querySelectorAll('form, input[name], button');
// the NodeList of elements
// CSS Selector via CSSselect
```
### What's New
* in `v0.11` a new `linkedom/worker` export has been added. This works with [deno](https://deno.land/), Web, and Service Workers, and it's not strictly coupled with NodeJS. Please note, this export does not include `canvas` module, and the `performance` is retrieved from the `globalThis` context.
### Serializing as JSON
*LinkeDOM* uses a blazing fast [JSDON serializer](https://github.com/WebReflection/jsdon#readme), and nodes, as well as whole documents, can be retrieved back via `parseJSON(value)`.
```js
// any node can be serialized
const array = toJSON(document);
// somewhere else ...
import {parseJSON} from 'linkedom';
const document = parseJSON(array);
```
Please note that *Custom Elements* won't be upgraded, unless the resulting nodes are imported via `document.importNode(nodeOrFragment, true)`.
Alternatively, `JSDON.fromJSON(array, document)` is able to initialize right away *Custom Elements* associated with the passed `document`.
### Simulating JSDOM Bootstrap
This module is based on [DOMParser](https://developer.mozilla.org/en-US/docs/Web/API/DOMParser) API, hence it creates a *new* `document` each time `new DOMParser().parseFromString(...)` is invoked.
As there's *no global pollution* whatsoever, to retrieve classes and features associated to the `document` returned by `parseFromString`, you need to access its `defaultView` property, which is a special proxy that lets you get *pseudo-global-but-not-global* properties and classes.
Alternatively, you can use the `parseHTML` utility which returns a pseudo *window* object with all the public references you need.
```js
// facade to a generic JSDOM bootstrap
import {parseHTML} from 'linkedom';
function JSDOM(html) { return parseHTML(html); }
// now you can do the same as you would with JSDOM
const {document, window} = new JSDOM('
Hello LinkeDOM 👋
');
```
## Data Structure
The triple-linked list data structure is explained below in [How does it work?](#how-does-it-work), the [Deep Dive](./deep-dive.md), and the [presentation on Speakeasy JS](https://www.youtube.com/watch?v=PEESaD7Qkxs).
## F.A.Q.
Why "not too close"?
*LinkeDOM* has zero intention to:
* implement all things *JSDOM* already implemented. If you need a library which goal is to be 100% standard compliant, please [use JSDOM](https://github.com/jsdom/jsdom) because *LinkeDOM* doesn't want to be neirly as bloated nor as slow as *JSDOM* is
* implement features not interesting for *Server Side Rendering*. If you need to pretend your NodeJS, Worker, or any other environment, is a browser, please [use JSDOM](https://github.com/jsdom/jsdom)
* other points listed, or not, in the followung *F.A.Q.s*: this project will always prefer the minimal/fast approach over 100% compliant behavior. Again, if you are looking for 100% compliant behavior and you are not willing to have any compromise in the DOM, this is **not** the project you are looking for
That's it, the rule of thumb is: do I want to be able to render anything, and as fast as possible, in a DOM-less env? *LinkeDOM* is great!
Do I need a 100% spec compliant env that simulate a browser? I rather use *cypress* or *JSDOM* then, as *LinkeDOM* is not meant to be a replacement for neither projects.
Are live collections supported?
The *TL;DR* answer is **no**. Live collections are considered legacy, are slower, have side effects, and it's not intention of *LinkeDOM* to support these, including:
* `getElementsByTagName` does not update when nodes are added or removed
* `getElementsByClassName` does not update when nodes are added or removed
* `childNodes`, if trapped once, does not update when nodes are added or removed
* `children`, if trapped once, does not update when nodes are added or removed
* `attributes`, if trapped once, does not update when attributes are added or removed
* `document.all`, if trapped once, does not update when attributes are added or removed
If any code you are dealing with does something like this:
```js
const {children} = element;
while (children.length)
target.appendChild(children[0]);
```
it will cause an infinite loop, as the `children` reference won't side-effect when nodes are moved.
You can solve this in various ways though:
```js
// the modern approach (suggested)
target.append(...element.children);
// the check for firstElement/Child approach (good enough)
while (element.firstChild)
target.appendChild(element.firstChild);
// the convert to array approach (slow but OK)
const list = [].slice.call(element.children);
while (list.length)
target.appendChild(list.shift());
// the zero trap approach (inefficient)
while (element.childNodes.length)
target.appendChild(element.childNodes[0]);
```
Are childNodes and children always same?
**Nope**, these are discovered each time, so when heavy usage of these *lists* is needed, but no mutation is meant, just trap these once and use these like a frozen array.
```js
function eachChildNode({childNodes}, callback) {
for (const child of childNodes) {
callback(child);
if (child.nodeType === child.ELEMENT_NODE)
eachChildNode(child, callback);
}
}
eachChildNode(document, console.log);
```
## How does it work?
All nodes are linked on both sides, and all elements consist of 2 nodes, also linked in between.
Attributes are always at the beginning of an element, while zero or more extra nodes can be found before the end.
A fragment is a special element without boundaries, or parent node.
```
Node: ← node →
Attr: ← attr → ↑ ownerElement?
Text: ← text → ↑ parentNode?
Comment: ← comment → ↑ parentNode?
Element: ← start ↔ end → ↑ parentNode?
Fragment: start ↔ end
Element example:
parentNode? (as shortcut for a linked list of previous nodes)
↑
├────────────────────────────────────────────┐
│ ↓
node? ← start → attr* → text* → comment* → element* → end → node?
↑ │
└────────────────────────────────────────────┘
Fragment example:
┌────────────────────────────────────────────┐
│ ↓
start → attr* → text* → comment* → element* → end
↑ │
└────────────────────────────────────────────┘
```
If this is not clear, feel free to **[read more in the deep dive page](./deep-dive.md)**.
### Why is this better?
Moving *N* nodes from a container, being it either an *Element* or a *Fragment*, requires the following steps:
* update the first *left* link of the moved segment
* update the last *right* link of the moved segment
* connect the *left* side, if any, of the moved node at the beginning of the segment, with the *right* side, if any, of the node at the end of such segment
* update the *parentNode* of the segment to either *null*, or the new *parentNode*
As result, there are no array operations, and no memory operations, and everything is kept in sync by updating a few properties, so that removing `3714` sparse `
` elements in a *12M* document, as example, takes as little as *3ms*, while appending a whole fragment takes close to *0ms*.
Try `npm run benchmark:html` to see it yourself.
This structure also allows programs to avoid issues such as "*Maximum call stack size exceeded*" (basicHTML), or "*JavaScript heap out of memory*" crashes (JSDOM), thanks to its reduced usage of memory and zero stacks involved, hence scaling better from small to very big documents.
### Are *childNodes* and *children* always computed?
As everything is a `while(...)` loop away, by default this module does not cache anything, specially because caching requires state invalidation for each container, returned queries, and so on. However, you can import `linkedom/cached` instead, as long as you [understand its constraints](https://github.com/WebReflection/linkedom#cached-vs-not-cached).
## Parsing VS Node Types
This module parses, and works, only with the following `nodeType`:
* `ELEMENT_NODE`
* `ATTRIBUTE_NODE`
* `TEXT_NODE`
* `COMMENT_NODE`
* `DOCUMENT_NODE`
* `DOCUMENT_FRAGMENT_NODE`
* `DOCUMENT_TYPE_NODE`
Everything else, at least for the time being, is considered *YAGNI*, and it won't likely ever land in this project, as there's no goal to replicate deprecated features of this aged Web.
## Cached VS Not Cached
This module exports both `linkedom` and `linkedom/cached`, which are basically the exact same thing, except the cached version outperforms `linkedom` in these scenarios:
* the document, or any of its elements, are rarely changed, as opposite of frequently mutated or manipulated
* the use-case needs many repeated *CSS* selectors, over a sporadically mutated "*tree*"
* the generic DOM mutation time is *not* a concern (each, removal or change requires a whole document cache invalidation)
* the *RAM* is *not* a concern (all cached results are held into *NodeList* arrays until changes happen)
On the other hand, the basic, *non-cached*, module, grants the following:
* minimal amount of *RAM* needed, given any task to perform, as nothing is ever retained on *RAM*
* linear fast performance for any *every-time-new* structure, such as those created via `importNode` or `cloneNode` (i.e. template literals based libraries)
* much faster DOM manipulation, without side effect caused by cache invalidation
## Benchmarks
To run the benchmark locally, please follow these commands:
```sh
git clone https://github.com/WebReflection/linkedom.git
cd linkedom/test
npm i
cd ..
npm i
npm run benchmark
```