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#html-templating #html-rendering #control-flow #language #natural #html-first

bin+lib platelet

HTML-first templating language

by angusjf

3 releases

0.1.2 Jun 6, 2024
0.1.1 Jun 6, 2024
0.1.0 Jun 6, 2024

#94 in Template engine

MIT license

110KB
3K SLoC

platelet

platelet is an HTML-first templating language.

This repo contains a Rust library for rendering platelet templates.

Why platelet?

Unlike moustache, handlebars, Jinja, Liquid and other templating languages, platelet's syntax is part of HTML (similar to Vue.js).

This has a few upsides:

  • Higher level but less powerful than direct string manipulation
  • The language is natural to read and write when working with HTML, and control flow follows HTML structure
  • You can use your own HTML formatters and tooling
  • HTML sanitization is more natural and straightforward

Example

You can explore live examples in the platelet playground

Template
<ul pl-if="n > 0">
  <li pl-for="i in [1, 2, 3]">{{ i }} × {{ n }} = {{ i * n }}</li>
</ul>
Context (input)
{ "n": 7 }
Output
<ul>
  <li>1 × 7 = 7</li>
  <li>2 × 7 = 14</li>
  <li>3 × 7 = 21</li>
</ul>
More examples

Advanced example

Template templates/index.html
<!doctype html>
<html>
  <head>
    <title>{{ title }}</title>
  </head>
  <body>
    <template pl-for="b in blogposts" pl-src="./blogpost.html" ^blogpost="b">
    </template>
  </body>
</html>
Template templates/blogpost.html
<article>
  <img ^src="blogpost.img_url" />
  <div>
    <h2>
      <a ^href="blogpost.link">{{blogpost.title}}</a>
    </h2>
    <template pl-html="blogpost.summary"></template>
    <date>{{blogpost.date}}</date>
  </div>
</article>
<style>
  article {
    display: flex;
  }
</style>
Context (input)
{
  "title": "Angus' Blog",
  "blogposts": [
    {
      "img_url": "...",
      "link": "...",
      "summary": "...",
      "title": "...",
      "date": "01/11/2025"
    },
    {
      "img_url": "...",
      "link": "...",
      "summary": "...",
      "title": "...",
      "date": "01/11/2020"
    }
  ]
}

Reference

Syntax Example Details
pl- directives pl-if, pl-for ... →
^ attributes ^class, ^name ... →
{{ ... }} nodes {{ user.email }} →
Expressions 1 + users[i].score →

pl- Directives

HTML Attributes starting with a pl- are special. They are inspired by Vue's directives.

attribute
pl-if
pl-else-if
pl-else
pl-for
pl-html
pl-src
pl-slot
pl-is

Conditionals: pl-if, pl-else-if, pl-else

pl-if will only render this element if the expression is truthy

pl-else-if, used following a pl-if, will only render this element if the expression is truthy

pl-else, used following a pl-if or pl-else-if, will render this element otherwise

<button pl-if="stock >= 1">Add to cart</button>
<button pl-else-if="stock > 0">Add to cart (1 item left!)</button>
<button pl-else disabled>Out of stock</button>

If applied to a <template>, the template will be and the children rendered.

pl-for

Render element multiple times.

Allows 4 types of expression:

<div pl-for="item in items">{{item.text}}</div>
<div pl-for="(item, index) in items">...</div>
<div pl-for="(value, key) in object">...</div>
<div pl-for="(value, name, index) in object">...</div>

If applied to a <template>, the template will be removed and the children rendered.

pl-html

Set the innerHTML (without sanitization) to the given expression.

To set the outerHTML, apply this to a <template>.

<p pl-html="markdown"></p>

{ "markdown": "<h1>Content from a CMS</h1>..." }

pl-src

Given a path as a string, renders the template at the path and replaces the element.

<slot pl-src="./sidebar.html" ^username="data.username">
  <p>Some text...</p>
</slot>

The attributes set on the element (regular attributes or rendered ^ attributes) are used as the context for rendering the template.

pl-slot

On a <slot>, pl-slot (with an optional name) marks the element as a slot, to be replaced.

On a <template>, pl-slot marks the template content as "what fills that slot".

index.html
<slot pl-src="layout.html">
    <template pl-slot="sidebar">
        <ul> ...
    </template>
    <template pl-slot="content">
        <table> ...
    </template>
</slot>
layout.html
<body>
  <nav>
    <slot pl-slot="sidebar"></slot>
  </nav>
  <main>
    <slot pl-slot="content"></slot>
  </main>
</body>
Output
<body>
  <nav>
    <ul> ...
  </nav>
  <main>
    <table> ...
  </main>
</body>

pl-is

Replace the rendered element's tag with this element, given an expression that returns a string

<slot pl-is='i == 0 ? "h1" : "h2"'>{item}</slot>

^ Attributes

In an HTML attribute, prefixing the attribute with ^ allows you to set the value to a platelet expression.

<a ^href='"/products/" + slug'></a>

If the expression is false or null, the attribute will not render.

<div
  class="static"
  ^class="{ active: isActive, 'text-danger': hasError }"
  ^name="null"
></div>

This will render:

<div class="static active text-danger"></div>

Text Nodes

In an HTML text node, {{variable}} inserts a (sanitized) string.

<h1>Welcome back {{user.name}}!</h1>

If the variable is not defined then an error is returned.

Data type Rendered as
Number A number
String A string
Boolean true or false
Null blank
Array error
Object error

Expressions

All valid JSON values are valid platelet expressions. On top of this, single-quoted strings 'like this' are allowed for convenience when working with HTML.

Operators

On anything: ==, !=, &&, ||, !, x ? y : z

On numbers: + (addition) On strings and arrays: + (concatenation) On objects: + (shallow merge, right hand side overriding)

On numbers: -, *, /, % (mod)

On numbers: >, <, >=, <=

On objects arrays and strings, indexing operator a[b]

On objects, dot access: {"name": "angus"}.name

On arrays, objects and strings: len(z)

Expressions can be bracketed (9 + 3) / 2 == 6

Truthiness

false, [], "", {}, null are falsy.

All other values are truthy.

Dependencies

~7–13MB
~169K SLoC