TagSoup is [the fastest](#performance) pure JS SAX/DOM XML/HTML parser and serializer.
- Extremely low memory consumption.
- Tolerant of malformed tag nesting, missing end tags, etc.
- Recognizes CDATA sections, processing instructions, and DOCTYPE declarations.
- Supports both strict XML and forgiving HTML parsing modes.
- [20 kB gzipped](https://bundlephobia.com/result?p=tag-soup), including dependencies.
- Check out TagSoup dependencies: [Speedy Entities](https://github.com/smikhalevski/speedy-entities#readme)
and [Flyweight DOM](https://github.com/smikhalevski/flyweight-dom#readme).
```sh
npm install --save-prod tag-soup
```
- [API docs](https://smikhalevski.github.io/tag-soup/)
- [DOM parsing](#dom-parsing)
- [SAX parsing](#sax-parsing)
- [Tokenization](#tokenization)
- [Serialization](#serialization)
- [Parser options](#parser-options)
- [Performance](#performance)
- [Limitations](#limitations)
# DOM parsing
TagSoup exports preconfigured [`HTMLDOMParser`](https://smikhalevski.github.io/tag-soup/variables/HTMLDOMParser.html)
which parses HTML markup as a DOM node. This parser never throws errors during parsing and forgives malformed markup:
```ts
import { HTMLDOMParser, toHTML } from 'tag-soup';
const fragment = HTMLDOMParser.parseFragment('hello
cool');
// ⮕ DocumentFragment
toHTML(fragment);
// ⮕ '
hello
cool
'
```
`HTMLDOMParser` decodes both HTML entities and numeric character references with
[`decodeHTML`](https://smikhalevski.github.io/speedy-entities/variables/decodeHTML.html).
[`XMLDOMParser`](https://smikhalevski.github.io/tag-soup/variables/XMLDOMParser.html)
parses XML markup as a DOM node. It throws
[`ParserError`](https://smikhalevski.github.io/tag-soup/classes/ParserError.html) if markup doesn't satisfy XML spec:
```ts
import { XMLDOMParser, toXML } from 'tag-soup';
XMLDOMParser.parseFragment('hello');
// ❌ ParserError: Unexpected end tag.
const fragment = XMLDOMParser.parseFragment('
hello
');
// ⮕ DocumentFragment
toXML(fragment);
// ⮕ 'hello
'
```
`XMLDOMParser` decodes both XML entities and numeric character references with
[`decodeXML`](https://smikhalevski.github.io/speedy-entities/variables/decodeXML.html).
TagSoup uses [Flyweight DOM](https://github.com/smikhalevski/flyweight-dom#readme) nodes, which provide many standard
DOM manipulation features:
```ts
const document = HTMLDOMParser.parseDocument('hello');
document.doctype.name;
// ⮕ 'html'
document.textContent;
// ⮕ 'hello'
```
For example, you can use `TreeWalker` to traverse DOM nodes:
```ts
import { TreeWalker, NodeFilter } from 'flyweight-dom';
const fragment = XMLDOMParser.parseFragment('hello
');
const treeWalker = new TreeWalker(fragment, NodeFilter.SHOW_TEXT);
treeWalker.nextNode();
// ⮕ Text { 'hello' }
```
Create a custom DOM parser using
[`createDOMParser`](https://smikhalevski.github.io/tag-soup/functions/createDOMParser.html):
```ts
import { createDOMParser } from 'tag-soup';
const myParser = createDOMParser({
voidTags: ['br'],
});
myParser.parseFragment('
');
// ⮕ DocumentFragment
```
# SAX parsing
TagSoup exports preconfigured [`HTMLSAXParser`](https://smikhalevski.github.io/tag-soup/variables/HTMLSAXParser.html)
which parses HTML markup and calls handler methods when a token is read. This parser never throws errors during parsing
and forgives malformed markup:
```ts
import { HTMLSAXParser } from 'tag-soup';
HTMLSAXParser.parseFragment('hello
cool', {
onStartTagOpening(tagName) {
// Called with 'p', 'p', and 'br'
},
onText(text) {
// Called with 'hello' and 'cool'
},
});
```
[`XMLSAXParser`](https://smikhalevski.github.io/tag-soup/variables/XMLSAXParser.html) parses XML markup and calls
handler methods when a token is read. It throws
[`ParserError`](https://smikhalevski.github.io/tag-soup/classes/ParserError.html) if markup doesn't satisfy XML spec:
```ts
import { XMLSAXParser } from 'tag-soup';
XMLSAXParser.parseFragment('
hello', {});
// ❌ ParserError: Unexpected end tag.
XMLSAXParser.parseFragment('
hello
', {
onEndTag(tagName) {
// Called with 'br' and 'p'
},
});
```
Create a custom SAX parser using
[`createSAXParser`](https://smikhalevski.github.io/tag-soup/functions/createSAXParser.html):
```ts
import { createSAXParser } from 'tag-soup';
const myParser = createSAXParser({
voidTags: ['br'],
});
myParser.parseFragment('
', {
onStartTagOpening(tagName) {
// Called with 'p' and 'br'
},
});
```
## SAX handler callbacks
The [`SAXHandler`](https://smikhalevski.github.io/tag-soup/interfaces/SAXHandler.html) defines the following optional
callbacks. Implement only the ones you need.
| Callback | Description |
| :---------------------------------------------------------------------------------------------------------------------- | :--------------------------------------------- |
| [`onStartTagOpening`](https://smikhalevski.github.io/tag-soup/interfaces/SAXHandler.html#onstarttagopening) | A start tag name is read. |
| [`onAttribute`](https://smikhalevski.github.io/tag-soup/interfaces/SAXHandler.html#onattribute) | An attribute and its decoded value were read. |
| [`onStartTagClosing`](https://smikhalevski.github.io/tag-soup/interfaces/SAXHandler.html#onstarttagclosing) | A start tag is closed `>`. |
| [`onStartTagSelfClosing`](https://smikhalevski.github.io/tag-soup/interfaces/SAXHandler.html#onstarttagselfclosing) | A start tag is self-closed `/>`. |
| [`onStartTag`](https://smikhalevski.github.io/tag-soup/interfaces/SAXHandler.html#onstarttag) | A start tag and its atributes were read. |
| [`onEndTag`](https://smikhalevski.github.io/tag-soup/interfaces/SAXHandler.html#onendtag) | An end tag matching an open start tag is read. |
| [`onText`](https://smikhalevski.github.io/tag-soup/interfaces/SAXHandler.html#ontext) | A decoded text content is read. |
| [`onComment`](https://smikhalevski.github.io/tag-soup/interfaces/SAXHandler.html#oncomment) | A comment is read. |
| [`onDoctype`](https://smikhalevski.github.io/tag-soup/interfaces/SAXHandler.html#ondoctype) | A DOCTYPE declaration is read. |
| [`onCDATASection`](https://smikhalevski.github.io/tag-soup/interfaces/SAXHandler.html#oncdatasection) | A CDATA section is read. |
| [`onProcessingInstruction`](https://smikhalevski.github.io/tag-soup/interfaces/SAXHandler.html#onprocessinginstruction) | A processing instruction is read. |
Example using several callbacks at once:
```ts
import { HTMLSAXParser } from 'tag-soup';
HTMLSAXParser.parseFragment('hello
', {
onComment(data) {
// Called with ' greeting '
},
onStartTagOpening(tagName) {
// Called with 'p'
},
onAttribute(name, value) {
// Called with 'class', 'x'
},
onStartTagClosing() {
// Called after all attributes of 'p' are read
},
onStartTag(tagName, attributes, isSelfClosing) {
// Called after onStartTagClosing
},
onText(text) {
// Called with 'hello'
},
onEndTag(tagName) {
// Called with 'p'
},
});
```
# Tokenization
TagSoup exports preconfigured
[`HTMLTokenizer`](https://smikhalevski.github.io/tag-soup/variables/HTMLSAXParser.html) which parses HTML markup and
invokes a callback when a token is read. This tokenizer never throws errors during tokenization and forgives malformed
markup:
```ts
import { HTMLTokenizer } from 'tag-soup';
HTMLTokenizer.tokenizeFragment('hello
cool', (token, startIndex, endIndex) => {
// Handle token
});
```
[`XMLTokenizer`](https://smikhalevski.github.io/tag-soup/variables/XMLTokenizer.html) parses XML markup and invokes
a callback when a token is read. It throws
[`ParserError`](https://smikhalevski.github.io/tag-soup/classes/ParserError.html) if markup doesn't satisfy XML spec:
```ts
import { XMLTokenizer } from 'tag-soup';
XMLTokenizer.tokenizeFragment('
hello', (token, startIndex, endIndex) => {});
// ❌ ParserError: Unexpected end tag.
XMLTokenizer.tokenizeFragment('
hello
', (token, startIndex, endIndex) => {
// Handle token
});
```
Create a custom tokenizer using
[`createTokenizer`](https://smikhalevski.github.io/tag-soup/functions/createTokenizer.html):
```ts
import { createTokenizer } from 'tag-soup';
const myTokenizer = createTokenizer({
voidTags: ['br'],
});
myTokenizer.tokenizeFragment('
', (token, startIndex, endIndex) => {
// Handle token
});
```
The [`Token`](https://smikhalevski.github.io/tag-soup/types/Token.html) passed to the callback is one of the
following string literals. `startIndex` and `endIndex` are the character positions of the token's value in the input.
| Token | Description |
| :-------------------------------- | :------------------------------------------------------------------- |
| `"TEXT"` | Text content between tags. |
| `"START_TAG_NAME"` | The name portion of an opening tag, e.g. `p` in ``. |
| `"START_TAG_CLOSING"` | The `>` that closes an opening tag. |
| `"START_TAG_SELF_CLOSING"` | The `/>` that self-closes a tag. |
| `"END_TAG_NAME"` | The name portion of a closing tag, e.g. `p` in `
`. |
| `"ATTRIBUTE_NAME"` | An attribute name. |
| `"ATTRIBUTE_VALUE"` | A decoded attribute value. |
| `"COMMENT"` | Comment content, excluding ``. |
| `"PROCESSING_INSTRUCTION_TARGET"` | The target of a processing instruction, e.g. `xml` in ``. |
| `"PROCESSING_INSTRUCTION_DATA"` | The data portion of a processing instruction. |
| `"CDATA_SECTION"` | Content of a CDATA section, excluding ``. |
| `"DOCTYPE_NAME"` | The name in a DOCTYPE declaration, e.g. `html` in ``. |
# Serialization
TagSoup exports two preconfigured serializers:
[`toHTML`](https://smikhalevski.github.io/tag-soup/variables/toHTML.html) and
[`toXML`](https://smikhalevski.github.io/tag-soup/variables/toXML.html).
```ts
import { HTMLDOMParser, toHTML } from 'tag-soup';
const fragment = HTMLDOMParser.parseFragment('hello
cool');
// ⮕ DocumentFragment
toHTML(fragment);
// ⮕ '
hello
cool
'
```
Create a custom serializer using
[`createSerializer`](https://smikhalevski.github.io/tag-soup/functions/createSerializer.html):
```ts
import { HTMLDOMParser, createSerializer } from 'tag-soup';
const mySerializer = createSerializer({
voidTags: ['br'],
});
const fragment = HTMLDOMParser.parseFragment('hello');
// ⮕ DocumentFragment
mySerializer(fragment);
// ⮕ '
hello
'
```
[`SerializerOptions`](https://smikhalevski.github.io/tag-soup/interfaces/SerializerOptions.html) accepts the
following properties:
| Option | Description |
| :-------------------------------------------------------------------------------------------------------------------------------------- | :---------------------------------------------------------------- |
| [`voidTags`](https://smikhalevski.github.io/tag-soup/interfaces/SerializerOptions.html#voidtags) | Tags that have no content and no closing tag (e.g. `br`, `img`). |
| [`encodeText`](https://smikhalevski.github.io/tag-soup/interfaces/SerializerOptions.html#encodetext) | Callback to encode text content and attribute values. |
| [`areSelfClosingTagsSupported`](https://smikhalevski.github.io/tag-soup/interfaces/SerializerOptions.html#areselfclosingtagssupported) | If `true`, void tags are serialized as `
` instead of `
`. |
| [`areTagNamesCaseInsensitive`](https://smikhalevski.github.io/tag-soup/interfaces/SerializerOptions.html#aretagnamescaseinsensitive) | If `true`, tag name comparisons are case-insensitive. |
Serialize XML with entity encoding:
```ts
import { XMLDOMParser, createSerializer } from 'tag-soup';
import { encodeXML } from 'speedy-entities';
const toXMLEncoded = createSerializer({
areSelfClosingTagsSupported: true,
encodeText: encodeXML,
});
const fragment = XMLDOMParser.parseFragment('AT&T');
toXMLEncoded(fragment);
// ⮕ 'AT&T'
```
# Parser options
`createDOMParser`, `createSAXParser`, and `createTokenizer` accept a
[`ParserOptions`](https://smikhalevski.github.io/tag-soup/interfaces/ParserOptions.html) object.
| Option | Description |
| :--------------------------------------------------------------------------------------------------------------------------------------------------------- | :----------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| [`voidTags`](https://smikhalevski.github.io/tag-soup/interfaces/ParserOptions.html#voidtags) | Tags that have no content and no end tag (e.g. `br`, `img`). See [HTML5 Void Elements](https://www.w3.org/TR/2010/WD-html5-20101019/syntax.html#void-elements). |
| [`rawTextTags`](https://smikhalevski.github.io/tag-soup/interfaces/ParserOptions.html#rawtexttags) | Tags whose content is treated as raw text (e.g. `script`, `style`). See [HTML5 Raw Text Elements](https://www.w3.org/TR/2010/WD-html5-20101019/syntax.html#raw-text-elements). |
| [`foreignTags`](https://smikhalevski.github.io/tag-soup/interfaces/ParserOptions.html#foreigntags) | Map from a tag to tokenizer options that are applied inside the tag. |
| [`decodeText`](https://smikhalevski.github.io/tag-soup/interfaces/ParserOptions.html#decodetext) | Callback to decode text content and attribute values (e.g. `decodeHTML` from `speedy-entities`). |
| [`implicitlyClosedTags`](https://smikhalevski.github.io/tag-soup/interfaces/ParserOptions.html#implicitlyclosedtags) | Map from a tag to the list of open tags it implicitly closes. For example `{ h1: ['p'] }` means an opening `` closes any currently open `
`. |
| [`implicitlyOpenedTags`](https://smikhalevski.github.io/tag-soup/interfaces/ParserOptions.html#implicitlyopenedtags) | Tags for which a synthetic start tag is inserted when an unbalanced end tag is encountered (e.g. `['p', 'br']` so `
` becomes ``). |
| [`areTagNamesCaseInsensitive`](https://smikhalevski.github.io/tag-soup/interfaces/ParserOptions.html#aretagnamescaseinsensitive) | If `true`, tag name comparisons ignore ASCII case. |
| [`areCDATASectionsRecognized`](https://smikhalevski.github.io/tag-soup/interfaces/ParserOptions.html#arecdatasectionsrecognized) | If `true`, CDATA sections (``) are recognized. |
| [`areProcessingInstructionsRecognized`](https://smikhalevski.github.io/tag-soup/interfaces/ParserOptions.html#areprocessinginstructionsrecognized) | If `true`, processing instructions (``) are recognized. |
| [`areSelfClosingTagsRecognized`](https://smikhalevski.github.io/tag-soup/interfaces/ParserOptions.html#areselfclosingtagsrecognized) | If `true`, self-closing tags (`
`) are recognized; otherwise treated as start tags. |
| [`isStrict`](https://smikhalevski.github.io/tag-soup/interfaces/ParserOptions.html#isstrict) | If `true`, tag names and attributes are validated against XML constraints. |
| [`areUnbalancedEndTagsIgnored`](https://smikhalevski.github.io/tag-soup/interfaces/ParserOptions.html#areunbalancedendtagsignored) | If `true`, end tags without a matching start tag are silently dropped instead of throwing. |
| [`areUnbalancedStartTagsImplicitlyClosed`](https://smikhalevski.github.io/tag-soup/interfaces/ParserOptions.html#areunbalancedstarttagsimplicitlyclosed) | If `true`, unclosed start tags are forcefully closed at the end of their parent. |
A parser that mimics browser HTML behavior:
```ts
import { createDOMParser } from 'tag-soup';
import { decodeHTML } from 'speedy-entities';
const myParser = createDOMParser({
voidTags: [
'area',
'base',
'br',
'col',
'embed',
'hr',
'img',
'input',
'link',
'meta',
'param',
'source',
'track',
'wbr',
],
rawTextTags: ['script', 'style'],
decodeText,
areTagNamesCaseInsensitive: true,
areUnbalancedEndTagsIgnored: true,
areUnbalancedStartTagsImplicitlyClosed: true,
implicitlyClosedTags: {
h1: ['p'],
h2: ['p'],
li: ['li'],
dt: ['dd', 'dt'],
dd: ['dd', 'dt'],
},
foreignTags: {
svg: {
areCDATASectionsRecognized: true,
areProcessingInstructionsRecognized: true,
areSelfClosingTagsRecognized: true,
},
math: {
areCDATASectionsRecognized: true,
areProcessingInstructionsRecognized: true,
areSelfClosingTagsRecognized: true,
},
},
});
```
# Performance
Execution performance is measured in operations per second (± 5%), the higher number is better.
Memory consumption (RAM) is measured in bytes, the lower number is better.
| Library |
Library size |
DOM parsing |
SAX parsing |
| Ops/sec |
RAM |
Ops/sec |
RAM |
| tag-soup@3.2.1 |
21 kB
|
35 Hz |
22 MB |
54 Hz |
22 kB |
|
htmlparser2@12.0.0
|
34 kB
|
15 Hz |
35 MB |
24 Hz |
6 MB |
|
parse5@8.0.0
|
45 kB
|
7 Hz |
105 MB |
11 Hz |
10 MB |
Performance was measured when parsing [the 3.64 MB HTML file](./src/test/test.html).
Tests were conducted using [TooFast](https://github.com/smikhalevski/toofast#readme) on Apple M1 with Node.js v25.6.0.
To reproduce [the performance test suite](./src/test/perf/overall.perf.js) results, clone this repo and run:
```shell
npm ci
npm run build
npm run perf
```
# Limitations
TagSoup doesn't resolve some quirky element structures that malformed HTML may cause.
Assume the following markup:
```html
okay
nope
```
With [`DOMParser`](https://developer.mozilla.org/en-US/docs/Web/API/DOMParser) this markup would be transformed to:
```html
okay
nope
```
TagSoup doesn't insert the second `strong` tag:
```html
okay
nope
```