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html-frontmatter

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Extract key-value metadata from HTML comments

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# HTML Frontmatter

Extract key-value metadata from HTML comments

In the world of printed books, [front
matter](http://en.wikipedia.org/wiki/Book_design#Front_matter) is the stuff
at the beginning of the book like the title page, foreword, preface, table
of contents, etc. In the world of computer programming, frontmatter is metadata at the top
of a file. The term was (probably) popularized by the [Jekyll static site
generator](http://jekyllrb.com/docs/frontmatter/).

Unlike YAML frontmatter though, HTML frontmatter lives inside plain old HTML comments, so it will be
quietly ignored by tools/browsers that don't know about it.

## Installation

Download node at [nodejs.org](http://nodejs.org) and install it, if you haven't already.

```sh
npm install html-frontmatter --save
```

## Usage

Given an HTML or Markdown file that looks like this:

```html

<h1>Hello World</h1>
```

And code like this:

```js
var fm = require('html-frontmatter')
var frontmatter = fm(fs.readFileSync('github.md', 'utf-8'))
```

Here's what you'll get:

```js
{
  title: "GitHub Integration",
  keywords: "github, git, npm, enterprise",
  published: "Wed Oct 01 2014 17:00:00 GMT-0700 (PDT)",
  description: "npmE works with GitHub!"
}
```

### Multiline Values

If you have a long string (like a description) and want it to span multiple
lines, simply indent each subsequent line with *2 or more* spaces:

```html

```

### Colons in Values

Your values can contain colons. No worries.

```html

```

### Array Values

Your values can include shallow arrays

```html

```

Is equivalent to:

```html

```

And will return:

```js
{
  title: "This post has tags",
  tags: [100, 'this is a string', true]
}
```

### Coercion

- Boolean "true" and "false" strings are converted to Boolean.
- Numeric strings are converted to Number.
- Strings in [YMD-ish format](https://github.com/borgar/dateutil#dateutilparse-string-)
are converted to Date objects.

### Under the Hood

html-frontmatter exposes the regular expression it uses to detect presence
of frontmatter as a property named `pattern`. You can use it to
conditionally parse frontmatter:

```js
var fm = require('html-frontmatter')
var content = "A string that doesn't have frontmatter in it"
if (content.match(fm.pattern)) {
  // nope
}
```

## Tests

```sh
npm install
npm test

# ✓ extracts metadata from colon-delimited comments at the top of an HTML string
# ✓ returns null if frontmatter is not found
# ✓ handles values that contain colons
# ✓ handles line-wrapped values
# ✓ cleans up excess whitespace
# ✓ ignores comments that are not at the top of the file
# ✓ allows newlines before comments
# ✓ ignores comment lines starting with hashes (#)
# ✓ allows single-line comments
# ✓ does not include additional comments
# ✓ coerces boolean strings into Booleans
# ✓ coerces numeric strings into Numbers
# ✓ coerces YMD-ish date strings into Dates
# ✓ exposes its regex pattern as `pattern`
# ✓ handles missing right-hand-value
# ✓ handles shallow arrays
```

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