μXML

Minimal and fast non-validating SAX-like XML reader.

• When to use it:
  • You just need to communicate with XML-based API.
  • You just need to read XML-based configs or whatever.
  • You don’t care of ill-formed or invalid markup.
  • You don’t care of comments and processing instructions.
  • You don’t care of source locations.
• When NOT to use it:
  • You need to parse HTML, SVG, JSX, templates, etc.
  • You need to validate, debug, or format XML.
  • You need to handle comments and/or processing instructions.
  • You need to read XML streamingly.

Usage

yarn add microxml

npm install microxml

import { fast_xml, FastBackend } from 'microxml';

class ExampleBackend implements FastBackend {
    /** A table of entity definitions. */
    defs = new Map([
        ['foo', '"&bar;"'],
        ['bar', '<baz/>'],
    ]);

    /** Handle `<?xml...?>` and `<!DOCTYPE>`. */
    async head(text: string) {
        console.log('prolog %o', text);
    }

    otag(tag: string, attrs: Map<string, string>) {
        console.log('opening tag %o %o', tag, attrs);
    }

    ctag(tag: string) {
        console.log('closing tag %o', tag);
    }

    text(text: string) {
        console.log('text %o', text);
    }
}

const src = `
    <?xml version="1.0" encoding="UTF-8"?>
    <!DOCTYPE example>
    <test a="&foo;">
        &foo;
    </test>
`;

fast_xml(src, new ExampleBackend());

Features and non-features

• The fastest¹.
• The smallest¹ (≈1.5kB minified, no gzip).
• The smartest.
• The strongest.
• Unlike many others, DOES reparse entity replacements:
  • With x=<b>&y;</b>, y="<c/>":
    • <a>&x;</a>≡<a><b>"<c/>"</b></a>,
    • <a b="&x;" />≡<a b='<b>"<c/>"</b>'/>.
• May or may not explode in your face at ill-formed code.
• May or may not explode in your face at invalid code.
• Doesn’t parse <?xml...?> and <!DOCTYPE> declarations.
  • But the async head(text: string) hook may do the trick.
• Doesn’t parse HTML.
• Doesn’t parse SVG.
• Doesn’t parse JSX.
• Doesn’t parse templates.
• Doesn’t handle boolean and unquoted attributes <a b c=d>.
• Doesn’t handle references without the trailing semicolon &ampwtf.
• Doesn’t handle tags without the name <></>.
• Doesn’t handle tags like <script> and <style>.
• Doesn’t handle void tags differently.
• Doesn’t read streaming inputs.
• Doesn’t report source locations.
• Doesn’t report errors.
• Doesn’t trim nor collapse whitespace.
  • But merges adjacent text chunks.
• Silently ignores comments and processing instructions.
• Silently ignores undefined entities.
• Silently ignores text before the first tag.
• Silently ignores text after the last tag.
• Silently aborts at EOF-terminated attributes and attribute lists.
• Silently aborts at expansion of unterminated attribute lists.

---

1. [↑], [↑] Probably.

API

fast_xml(src, impl)

Read an XML document using the provided implementation.

Arguments:

• src: string — the XML document source string.
• impl: FastBackend — the backend to use.

Return:

• Promise<void> — a promise that resolves on error or document end.

FastBackend

A backend that provides entities table and token hooks.

All the properties and hooks are assumed to be mutable.

All the hooks are called as methods, so it’s safe to use this in them.

defs

The entity definitions table.

Type:

• Map<string, string>,
• undefined.

Keys are entity names without leading & and trailing ;.

Values are replacements, that are allowed to include markup and other references. When an entity is referenced in the markup mode, its replacement will be reparsed as markup with both tags, comments, entity references, etc. handled as usual. When an entity is referenced in an attribute value, everything except other references is ignored, including ["'] delimiters that normally terminate the attribute value.

When filling the table from <!DOCTYPE> and/or external DTDs, be careful to expand numeric references and parametric entities %...; before adding entries to the table.

The table is never consulted for numeric and predefined entities:

• &#...;,
• &#x...;,
• <,
• >,
• &,
• ',
• ".

The table is assumed to be mutable, so it’s safe to update or completely replace it anytime you want.

head(head)

XML prolog hook.

Triggered even if there is no prolog, or it doesn’t include the <?xml...?> or <!DOCTYPE> declaration.

Use it to parse the XML declaration and doctype.

The hook can return promise we’ll await, so you can do some async stuff here.

Arguments:

• head: string — the XML prolog text.

Return:

• any — anything you want, possibly awaitable.

otag(tag, attrs)

Opening tag hook. Also triggered for void tags.

Arguments:

• tag: string — the tag name.
• attrs: Map<string, string> — the attributes map.

Return:

• any — the return value is ignored.

ctag(tag)

Closing tag hook. For void tags, triggered immediately after the otag hook.

Arguments:

• tag: string — the tag name.

Return:

• any — the return value is ignored.

text(text)

Plain text hook.

Triggered immediately before otag or ctag with all pending plain text and <![CDATA[...]]> chunks merged, and only if the merged text is non-empty.

For example, when parsing a document like <a>b<!--x-->c<?y?>d<![CDATA[e]]>f</a>, we’ll only trigger text once with the bcdef argument.

Arguments:

• text: string — the plain text string.

Return:

• any — the return value is ignored.

License

MIT © 2023 Yuri Zemskov