micromark-extension-gfm-table

micromark extensions to support GFM tables.

Contents

• What is this?
• When to use this
• Install
• Use
• API
  • gfmTable()
  • gfmTableHtml()
• Bugs
• Authoring
• HTML
• CSS
• Syntax
• Types
• Compatibility
• Security
• Related
• Contribute
• License

What is this?

This package contains extensions that add support for the table syntax enabled by GFM to micromark. These extensions match github.com.

When to use this

This project is useful when you want to support tables in markdown.

You can use these extensions when you are working with micromark. To support all GFM features, use micromark-extension-gfm instead.

When you need a syntax tree, combine this package with mdast-util-gfm-table.

All these packages are used in remark-gfm, which focusses on making it easier to transform content by abstracting these internals away.

Install

This package is ESM only. In Node.js (version 16+), install with npm:

npm install micromark-extension-gfm-table

In Deno with esm.sh:

import {gfmTable, gfmTableHtml} from 'https://esm.sh/micromark-extension-gfm-table@2'

In browsers with esm.sh:

<script type="module">
  import {gfmTable, gfmTableHtml} from 'https://esm.sh/micromark-extension-gfm-table@2?bundle'
</script>

Use

import {micromark} from 'micromark'
import {gfmTable, gfmTableHtml} from 'micromark-extension-gfm-table'

const output = micromark('| a |\n| - |', {
  extensions: [gfmTable()],
  htmlExtensions: [gfmTableHtml()]
})

console.log(output)

Yields:

<table>
<thead>
<tr>
<th>a</th>
</tr>
</thead>
</table>

API

This package exports the identifiers gfmTable and gfmTableHtml. There is no default export.

The export map supports the development condition. Run node --conditions development module.js to get instrumented dev code. Without this condition, production code is loaded.

gfmTable()

Create an HTML extension for micromark to support GitHub tables syntax.

Returns

Extension for micromark that can be passed in extensions to enable GFM table syntax (Extension).

gfmTableHtml()

Create an HTML extension for micromark to support GitHub tables when serializing to HTML.

Returns

Extension for micromark that can be passed in htmlExtensions to support GFM tables when serializing to HTML (HtmlExtension).

Bugs

GitHub’s own algorithm to parse tables contains a bug. This bug is not present in this project. The issue relating to tables is:

• GFM tables: escaped escapes are incorrectly treated as escapes

Authoring

When authoring markdown with GFM tables, it’s recommended to always put pipes around cells. Without them, it can be hard to infer whether the table will work, how many columns there are, and which column you are currently editing.

It is recommended to not use many columns, as it results in very long lines, making it hard to infer which column you are currently editing.

For larger tables, particularly when cells vary in size, it is recommended not to manually “pad” cell text. While it can look better, it results in a lot of time spent realigning everything when a new, longer cell is added or the longest cell removed, as every row then must be changed. Other than costing time, it also causes large diffs in Git.

To illustrate, when authoring large tables, it is discouraged to pad cells like this:

| Alpha bravo charlie |              delta |
| ------------------- | -----------------: |
| Echo                | Foxtrot golf hotel |

Instead, use single spaces (and single filler dashes):

| Alpha bravo charlie | delta |
| - | -: |
| Echo | Foxtrot golf hotel |

HTML

GFM tables relate to several HTML elements: <table>, <tbody>, <td>, <th>, <thead>, and <tr>. See § 4.9.1 The table element, § 4.9.5 The tbody element, § 4.9.9 The td element, § 4.9.10 The th element, § 4.9.6 The thead element, and § 4.9.8 The tr element in the HTML spec for more info.

If the alignment of a column is left, right, or center, a deprecated align attribute is added to each <th> and <td> element belonging to that column. That attribute is interpreted by browsers as if a CSS text-align property was included, with its value set to that same keyword.

CSS

The following CSS is needed to make tables look a bit like GitHub. For the complete actual CSS see sindresorhus/github-markdown-css

/* Light theme. */
:root {
  --color-canvas-default: #ffffff;
  --color-canvas-subtle: #f6f8fa;
  --color-border-default: #d0d7de;
  --color-border-muted: hsla(210, 18%, 87%, 1);
}

/* Dark theme. */
@media (prefers-color-scheme: dark) {
  :root {
    --color-canvas-default: #0d1117;
    --color-canvas-subtle: #161b22;
    --color-border-default: #30363d;
    --color-border-muted: #21262d;
  }
}

table {
  border-spacing: 0;
  border-collapse: collapse;
  display: block;
  margin-top: 0;
  margin-bottom: 16px;
  width: max-content;
  max-width: 100%;
  overflow: auto;
}

tr {
  background-color: var(--color-canvas-default);
  border-top: 1px solid var(--color-border-muted);
}

tr:nth-child(2n) {
  background-color: var(--color-canvas-subtle);
}

td,
th {
  padding: 6px 13px;
  border: 1px solid var(--color-border-default);
}

th {
  font-weight: 600;
}

table img {
  background-color: transparent;
}

Syntax

Tables form with the following BNF:

gfmTable ::= gfmTableHead 0*(eol gfmTableBodyRow)

; Restriction: both rows must have the same number of cells.
gfmTableHead ::= gfmTableRow eol gfmTableDelimiterRow

gfmTableRow ::= ["|"] gfmTableCell 0*("|" gfmTableCell) ["|"] *spaceOrTab
gfmTableCell ::= *spaceOrTab gfmTableText *spaceOrTab
gfmTableText ::= 0*(line - "\\" - "|" / "\\" ["\\" / "|"])

gfmTableDelimiterRow ::= ["|"] gfmTableDelimiterCell 0*("|" gfmTableDelimiterCell) ["|"] *spaceOrTab
gfmTableDelimiterCell ::= *spaceOrTab gfmTableDelimiterValue *spaceOrTab
gfmTableDelimiterValue ::= [":"] 1*"-" [":"]

As this construct occurs in flow, like all flow constructs, it must be followed by an eol (line ending) or eof (end of file).

The above grammar shows that basically anything can be a cell or a row. The main thing that makes something a row, is that it occurs directly before or after a delimiter row, or after another row.

It is not required for a table to have a body: it can end right after the delimiter row.

Each column can be marked with an alignment. The alignment marker is a colon (:) used before and/or after delimiter row filler. To illustrate:

| none | left | right | center |
| ---- | :--- | ----: | :----: |

The number of cells in the delimiter row, is the number of columns of the table. Only the head row is required to have the same number of cells. Body rows are not required to have a certain number of cells. For body rows that have less cells than the number of columns of the table, empty cells are injected. When a row has more cells than the number of columns of the table, the superfluous cells are dropped. To illustrate:

| a | b |
| - | - |
| c |
| d | e | f |

Yields:

<table>
<thead>
<tr>
<th>a</th>
<th>b</th>
</tr>
</thead>
<tbody>
<tr>
<td>c</td>
<td></td>
</tr>
<tr>
<td>d</td>
<td>e</td>
</tr>
</tbody>
</table>

Each cell’s text is interpreted as the text content type. That means that it can include constructs such as attention (emphasis, strong).

The grammar for cells prohibits the use of | in them. To use pipes in cells, encode them as a character reference or character escape: | (or |, |, |, |) or \|.

Escapes will typically work, but they are not supported in code (text) (and the math (text) extension). To work around this, GitHub came up with a rather weird “trick”. When inside a table cell and inside code, escaped pipes are decoded. To illustrate:

| Name | Character |
| - | - |
| Left curly brace | `{` |
| Pipe | `\|` |
| Right curly brace | `}` |

Yields:

<table>
<thead>
<tr>
<th>Name</th>
<th>Character</th>
</tr>
</thead>
<tbody>
<tr>
<td>Left curly brace</td>
<td><code>{</code></td>
</tr>
<tr>
<td>Pipe</td>
<td><code>|</code></td>
</tr>
<tr>
<td>Right curly brace</td>
<td><code>}</code></td>
</tr>
</tbody>
</table>

👉 Note: no other character can be escaped like this. Escaping pipes in code does not work when not inside a table, either.

Types

This package is fully typed with TypeScript. It exports no additional types.

Compatibility

Projects maintained by the unified collective are compatible with maintained versions of Node.js.

When we cut a new major release, we drop support for unmaintained versions of Node. This means we try to keep the current release line, micromark-extension-gfm-table@^2, compatible with Node.js 16.

This package works with micromark version 3 and later.

Security

This package is safe.

Related

• micromark-extension-gfm — support all of GFM
• mdast-util-gfm-table — support all of GFM in mdast
• mdast-util-gfm — support all of GFM in mdast
• remark-gfm — support all of GFM in remark

Contribute

See contributing.md in micromark/.github for ways to get started. See support.md for ways to get help.

This project has a code of conduct. By interacting with this repository, organization, or community you agree to abide by its terms.

License

MIT © Titus Wormer