HTMLRewriter_Developer Tools_Edge Application-Documentation

The HTMLRewriter class allows developers to build comprehensive and expressive HTML parsers within CDNetworks Edge Cloud Apps Functions. It provides a streamlined JavaScript API for parsing and transforming HTML, enabling developers to build highly functional applications with a jQuery-like experience directly within the functions.

To use the HTMLRewriter class, instantiate it once within your Worker script and attach various handlers using the on and onDocument functions.

Constructor

new HTMLRewriter().on('*', new ElementHandler()).onDocument(new DocumentHandler());

Global Types

The HTMLRewriter API consistently uses the following types for various properties and methods:

Content

Content inserted into the output stream should be a string.
ContentOptions

{ html: Boolean } Controls how the HTMLRewriter treats inserted content. If the html boolean is set to true, content is treated as raw HTML. If the html boolean is set to false or not provided, content is treated as text and proper HTML escaping is applied.

Handlers

The HTMLRewriter utilizes two types of handlers: element handlers and document handlers.

Element Handlers

An element handler responds to incoming elements when attached using the .on function of an HTMLRewriter instance. The element handler should respond to element, comments, and text. The following example processes div elements using an ElementHandler class.

class ElementHandler {
  element(element) {
    // An incoming element, such as `div`
    console.log(`Incoming element: ${element.tagName}`);
  }

  comments(comment) {
    // An incoming comment
  }

  text(text) {
    // An incoming piece of text
  }
}

async function handleRequest(req) {
  const res = await fetch(req);

  return new HTMLRewriter().on('div', new ElementHandler()).transform(res);
}

Document Handlers

A document handler represents the incoming HTML document. A number of functions can be defined on a document handler to query and manipulate a document’s doctype, comments, text, and end. Unlike an element handler, a document handler’s doctype, comments, text, and end functions are not scoped by a particular selector. These functions are called for all content on the page, including content outside the top-level HTML tag:

class DocumentHandler {
  doctype(doctype) {
    // An incoming doctype, such as <!DOCTYPE html>
  }

  comments(comment) {
    // An incoming comment
  }

  text(text) {
    // An incoming piece of text
  }

  end(end) {
    // The end of the document
  }
}

Async Handlers

All functions defined on both element and document handlers can return either void or a Promise<void>. Making your handler function async allows you to access external resources such as an API via fetch, Workers KV, Durable Objects, or the cache.

class UserElementHandler {
  async element(element) {
    let response = await fetch(new Request('/user'));

    // fill in user info using response
  }
}

async function handleRequest(req) {
  const res = await fetch(req);

  // run the user element handler via HTMLRewriter on a div with ID `user_info`
  return new HTMLRewriter().on('div#user_info', new UserElementHandler()).transform(res);
}

Element

The element argument, used only in element handlers, represents a DOM element. Several methods are available on an element to query and manipulate it:

Properties

tagName

The name of the tag, such as “h1” or “div”. This property can be assigned different values to modify an element’s tag.
attributes (read-only)

A [name, value] pair of the tag’s attributes.
removed

Indicates whether the element has been removed or replaced by one of the previous handlers.
namespaceURI

Represents the namespace URI of an element.

Methods

getAttribute(name):

Returns the value for a given attribute name on the element, or null if it is not found.
hasAttribute(name):

Returns a boolean indicating whether an attribute exists on the element.
setAttribute(name, value):

Sets an attribute to a provided value, creating the attribute if it does not exist.
removeAttribute(name):

Removes the attribute.
before(content, contentOptions):

Inserts content before the element. Refer to Global types for more information on Content and ContentOptions.
after(content, contentOptions):

Inserts content right after the element.
prepend(content, contentOptions):

Inserts content right after the start tag of the element.
append(content, contentOptions):

Inserts content right before the end tag of the element.
replace(content, contentOptions):

Removes the element and inserts content in its place.
setInnerContent(content, contentOptions):

Replaces the content of the element.
remove():

Removes the element with all its content.
removeAndKeepContent():

Removes the start and end tags of the element but keeps its inner content intact.
onEndTag(handler):

Registers a handler that is invoked when the end tag of the element is reached.

EndTag

The endTag argument, used only in handlers registered with element.onEndTag, is a limited representation of a DOM element.

Properties

name

The name of the tag, such as “h1” or “div”. This property can be assigned different values to modify an element’s tag.

Methods

before(content, contentOptions):

Inserts content right before the end tag.
after(content, contentOptions):

Inserts content right after the end tag. Refer to Global types for more information on Content and ContentOptions.
remove():

Removes the element with all its content.

Text Chunks

Due to CDNetworks’ zero-copy streaming parsing, text chunks are not equivalent to text nodes in the lexical tree. A lexical tree text node can be represented by multiple chunks as they arrive from the origin server.

Consider the markup: <div>Hey. How are you?</div>. The Worker script may not receive the entire text node from the origin at once. Instead, the text element handler will be invoked for each received part of the text node. For example, the handler might be invoked with “Hey. How ”, then “are you?”. When the last chunk arrives, the text’s lastInTextNode property will be set to true. Developers should ensure these chunks are concatenated together.

Properties

removed

Indicates whether the element has been removed or replaced by one of the previous handlers.
text (read-only)

The text content of the chunk. Could be empty if the chunk is the last chunk of the text node.
lastInTextNode (read-only)

Specifies whether the chunk is the last chunk of the text node.

Methods

before(content, contentOptions):

Inserts content before the element. Refer to Global types for more information on Content and ContentOptions.
after(content, contentOptions):

Inserts content right after the element.
replace(content, contentOptions):

Removes the element and inserts content in its place.
remove():

Removes the element with all its content.

Comments

The comments function on an element handler allows developers to query and manipulate HTML comment tags.

class ElementHandler {
  comments(comment) {
    // An incoming comment element, such as <!-- My comment -->
  }
}

Properties

comment.removed

Indicates whether the element has been removed or replaced by one of the previous handlers.
comment.text

The text of the comment. This property can be assigned different values to modify the comment’s text.

Methods

before(content, contentOptions):

Inserts content before the element. Refer to Global types for more information on Content and ContentOptions.
after(content, contentOptions):

Inserts content right after the element.
replace(content, contentOptions):

Removes the element and inserts content in its place.
remove():

Removes the element with all its content.

Doctype

The doctype function on a document handler allows developers to query a document’s doctype.

class DocumentHandler {
  doctype(doctype) {
    // An incoming doctype element, such as
    // <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
  }
}

Properties

doctype.name (read-only)

The doctype name.
doctype.publicId (read-only)

The quoted string in the doctype after the PUBLIC atom.
doctype.systemId (read-only)

The quoted string in the doctype after the SYSTEM atom or immediately after the publicId.

End

The end function on a document handler allows developers to append content to the end of a document.

class DocumentHandler {
  end(end) {
    // The end of the document
  }
}

Methods

append(content, contentOptions):

Inserts content after the end of the document. Refer to Global types for more information on Content and ContentOptions.

Selectors

Selectors are patterns used to select specific elements within an HTML document. The HTMLRewriter supports a wide range of CSS selectors. Here are some examples:

Selector	Description
`*`	Any element.
`E`	Any element of type `E`.
`E:nth-child(n)`	An `E` element, the nth child of its parent.
`E:first-child`	An `E` element, the first child of its parent.
`E:nth-of-type(n)`	An `E` element, the nth sibling of its type.
`E:first-of-type`	An `E` element, the first sibling of its type.
`E:not(s)`	An `E` element that does not match the selector `s`.
`E.warning`	An `E` element belonging to the class `warning`.
`E#myid`	An `E` element with ID equal to `myid`.
`E[foo]`	An `E` element with a `foo` attribute.
`E[foo="bar"]`	An `E` element whose `foo` attribute value is exactly equal to “bar”.
`E[foo~="bar"]`	An `E` element whose `foo` attribute value is a list of whitespace-separated values, one of which is exactly equal to “bar”.
`E[foo^="bar"]`	An `E` element whose `foo` attribute value begins exactly with the string “bar”.
`E[foo$="bar"]`	An `E` element whose `foo` attribute value ends exactly with the string “bar”.
`E[foo*="bar"]`	An `E` element whose `foo` attribute value contains the substring “bar”.
`E F`	An `F` element descendant of an `E` element.
`E > F`	An `F` element child of an `E` element.

Errors

If a handler throws an exception, parsing is immediately halted, the transformed response body is errored with the thrown exception, and the untransformed response body is canceled (closed). If the transformed response body was already partially streamed back to the client, the client will see a truncated response.

async function handle(request) {
  let oldResponse = await fetch(request);
  let newResponse = new HTMLRewriter()
    .on('*', {
      element(element) {
        throw new Error('A really bad error.');
      },
    })
    .transform(oldResponse);

  // At this point, an expression like `await newResponse.text()`
  // will throw `new Error("A really bad error.")`.
  // Thereafter, any use of `newResponse.body` will throw the same error,
  // and `oldResponse.body` will be closed.

  // Alternatively, this will produce a truncated response to the client:
  return newResponse;
}

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HTMLRewriter

Constructor

Global Types

Handlers

Element Handlers

Document Handlers

Async Handlers

Element

Properties

Methods

EndTag

Properties

Methods

Text Chunks

Properties

Methods

Comments

Properties

Methods

Doctype

Properties

End

Methods

Selectors

Errors

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