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htmljs-parser

htmljs-parser

HTML parsers written according to the HTML spec will interpret all attribute values as strings which makes it challenging to properly describe a value's type (boolean, string, number, array, etc.) or to provide a complex JavaScript expression as a value. The ability to describe JavaScript expressions within attributes is important for HTML-based template compilers.

For example, consider a HTML-based template that wishes to support a custom tag named <say-hello> that supports an attribute named message that can be a string literal or a JavaScript expression.

Ideally, the template compiler should be able to handle any of the following:

<say-hello message="Hello world!" />
<say-hello message=("Hello " + personName + "!") />
<say-hello message="Hello ${personName}!" />

This parser extends the HTML grammar to add these important features:

  • JavaScript expressions as attribute values
<say-hello message=("Hello " + personNamecount=2+2 large=true />
  • Placeholders in the content of an element
<div>
    Hello ${personName}
</div>
  • Placeholders within attribute value strings
<div data-message="Hello ${personName}!">
  • JavaScript flow-control statements within HTML elements
<div for(a in b) />
<div if(a === b) />
  • JavaScript flow-control statements as elements
<for (a in b)>
<if (a in b)>

Installation

npm install htmljs-parser

Usage

var parser = require('htmljs-parser').createParser({
    onText: function(event) {
        // Text within an HTML element 
        var value = event.value;
    },
 
    onPlaceholder: function(event) {
        //  ${<value>]} // escape = true 
        // $!{<value>]} // escape = false 
        var value = event.value; // String 
        var escaped = event.escaped; // boolean 
        var withinBody = event.withinBody; // boolean 
        var withinAttribute = event.withinAttribute; // boolean 
        var withinString = event.withinString; // boolean 
        var withinOpenTag = event.withinOpenTag; // boolean 
        var pos = event.pos; // Integer 
    },
 
    onCDATA: function(event) {
        // <![CDATA[<value>]]> 
        var value = event.value; // String 
        var pos = event.pos; // Integer 
    },
 
    onOpenTag: function(event) {
        var tagName = event.tagName; // String 
        var attributes = event.attributes; // Array 
        var argument = event.argument; // Object 
        var pos = event.pos; // Integer 
    },
 
    onCloseTag: function(event) {
        // close tag 
        var tagName = event.tagName; // String 
        var pos = event.pos; // Integer 
    },
 
    onDocumentType: function(event) {
        // Document Type/DTD 
        // <!<value>> 
        // Example: <!DOCTYPE html> 
        var value = event.value; // String 
        var pos = event.pos; // Integer 
    },
 
    onDeclaration: function(event) {
        // Declaration 
        // <?<value>?> 
        // Example: <?xml version="1.0" encoding="UTF-8" ?> 
        var value = event.value; // String 
        var pos = event.pos; // Integer 
    },
 
    onComment: function(event) {
        // Text within XML comment 
        var value = event.value; // String 
        var pos = event.pos; // Integer 
    },
 
    onScriptlet: function(event) {
        // Text within <% %> 
        var value = event.value; // String 
        var pos = event.pos; // Integer 
    },
 
    onError: function(event) {
        // Error 
        var message = event.message; // String 
        var code = event.code; // String 
        var pos = event.pos; // Integer 
    }
});
 
parser.parse(str);

Content Parsing Modes

The parser, by default, will look for HTML tags within content. This behavior might not be desirable for certain tags, so the parser allows the parsing mode to be changed (usually in response to an onOpenTag event).

There are three content parsing modes:

  • HTML Content (DEFAULT): The parser will look for any HTML tag and content placeholders while in this mode and parse opening and closing tags accordingly.

  • Parsed Text Content: The parser will look for the closing tag that matches the current open tag as well as content placeholders but all other content will be interpreted as text.

  • Static Text Content: The parser will look for the closing tag that matches the current open tag but all other content will be interpreted as raw text.

var htmljs = require('htmljs-parser');
var parser = htmljs.createParser({
    onOpenTag: function(event) {
        // open tag 
        switch(event.tagName) {
            case 'textarea':
                //fall through 
            case 'script':
                //fall through 
            case 'style':
                // parse the content within these tags but only 
                // look for placeholders and the closing tag. 
                parser.enterParsedTextContentState();
                break;
            case 'dummy'
                // treat content within <dummy>...</dummy> as raw 
                // text and ignore other tags and placeholders 
                parser.enterStaticTextContentState();
                break;
            default:
                // The parser will switch to HTML content parsing mode 
                // if the parsing mode is not explicitly changed by 
                // "onOpenTag" function. 
        }
    }
});
 
parser.parse(str);

Parsing Events

The htmljs-parser is an event-based parser which means that it will emit events as it is parsing the document. Events are emitted via calls to on<eventname> function which are supplied as properties in the options via call to require('htmljs-parser').createParser(options).

onOpenTag

The onOpenTag function will be called each time an opening tag is encountered.

EXAMPLE: Simple tag

INPUT:

<div>

OUTPUT EVENT:

{
    type: 'openTag',
    tagName: 'div',
    attributes: []
}

EXAMPLE: Tag with literal attribute values

INPUT:

<div class="demo" disabled=false data-number=123>

OUTPUT EVENT:

{
    type: 'openTag',
    tagName: 'div',
    attributes: [
        {
            name: 'class',
            value: '"demo"',
            literalValue: 'demo'
        },
        {
            name: 'disabled',
            value: 'false',
            literalValue: false
        },
        {
            name: 'data-number',
            value: '123',
            literalValue: 123
        }
    ]
}

EXAMPLE: Tag with expression attribute

INPUT:

<say-something message=("Hello "+data.name)/>

OUTPUT EVENT:

{
    type: 'openTag',
    tagName: 'div',
    attributes: [
        {
            name: 'message',
            value: '"Hello "+data.name'
        }
    ]
}

EXAMPLE: Tag with an argument

INPUT:

<for(var i = 0i < 10i++)>

OUTPUT EVENT:

{
    type: 'openTag',
    tagName: 'for',
    argument: {
        value: 'var i = 0; i < 10; i++',
        pos: ... // Integer 
    },
    attributes: []
}

EXAMPLE: Attribute with an argument

INPUT:

<div if(x > y)>

OUTPUT EVENT:

{
    type: 'openTag',
    tagName: 'div',
    attributes: [
        {
            name: 'if',
            argument: {
                value: 'x > y',
                pos: ... // Integer 
            }
        }
    ]
}

onCloseTag

The onCloseTag function will be called each time a closing tag is encountered.

EXAMPLE: Simple close tag

INPUT:

</div>

OUTPUT EVENT:

{
    type: 'closeTag',
    tagName: 'div'
}

onText

The onText function will be called each time within an element when textual data is encountered.

NOTE: Text within <![CDATA[ ]]> will be emitted via call to onCDATA.

EXAMPLE

In the following example code, the TEXT sequences will be emitted as text events.

INPUT:

Simple text

OUTPUT EVENT:

{
    type: 'text',
    value: 'Simple text'
}

onCDATA

The onCDATA function will be called when text within <![CDATA[ ]]> is encountered.

EXAMPLE:

INPUT:

<![CDATA[This is text]]>

OUTPUT EVENT:

{
    type: 'cdata',
    value: 'This is text'
}

onPlaceholder

The onPlaceholder function will be called each time a placeholder is encountered.

If the placeholder starts with the $!{ sequence then event.escape will be false.

If the placeholder starts with the ${ sequence then event.escape will be true.

Text within <![CDATA[ ]]> and <!-- --> will not be parsed so you cannot use placeholders for these blocks of code.

EXAMPLE:

INPUT:

${"This is an escaped placeholder"}
$!{"This is a non-escaped placeholder"}

OUTPUT EVENTS

${name}
{
    type: 'placeholder',
    value: 'name',
    escape: true
}

$!{name}
{
    type: 'placeholder',
    value: 'name',
    escape: true
}

NOTE: The escape flag is merely informational. The application code is responsible for interpreting this flag to properly escape the expression.

Here's an example of modifying the expression based on the event.escape flag:

onPlaceholder: function(event) {
    if (event.escape) {
        event.value = 'escapeXml(' + event.value + ')';
    }
}

onDocumentType

The onDocumentType function will be called when the document type declaration is encountered anywhere in the content.

EXAMPLE:

INPUT:

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0//EN">

OUTPUT EVENT:

{
    type: 'documentType',
    value: 'DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0//EN"'
}

onDeclaration

The onDeclaration function will be called when an XML declaration is encountered anywhere in the content.

EXAMPLE:

INPUT:

<?xml version="1.0" encoding="UTF-8"?>

OUTPUT EVENT:

{
    type: 'declaration',
    value: 'xml version="1.0" encoding="UTF-8"'
}

onComment

The onComment function will be called when text within <!-- --> is encountered.

EXAMPLE:

INPUT:

<!--This is a comment-->

OUTPUT EVENT:

{
    type: 'comment',
    value: 'This is a comment'
}

onScriptlet

The onScriptlet function will be called when text within <% %> is encountered.

EXAMPLE:

INPUT:

<% console.log("Hello World!"); %>

OUTPUT EVENT:

{
    type: 'scriptlet',
    value: ' console.log("Hello World!"); '
}

onError

The onError function will be called when malformed content is detected. The most common cause for an error is due to reaching the end of the input while still parsing an open tag, close tag, XML comment, CDATA section, DTD, XML declaration, or placeholder.

Possible error codes:

  • MISSING_END_TAG
  • MISSING_END_DELIMITER
  • MALFORMED_OPEN_TAG
  • MALFORMED_CLOSE_TAG
  • MALFORMED_CDATA
  • MALFORMED_PLACEHOLDER
  • MALFORMED_DOCUMENT_TYPE
  • MALFORMED_DECLARATION
  • MALFORMED_COMMENT
  • EXTRA_CLOSING_TAG
  • MISMATCHED_CLOSING_TAG
  • ...

EXAMPLE:

INPUT:

<a href="

OUTPUT EVENT:

{
    type: 'error',
    code: 'MALFORMED_OPEN_TAG',
    message: 'EOF reached while parsing open tag.',
    pos: 0,
    endPos: 9
}