runty

Extensible conditional string micro templates.

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Features

• Simple, but powerful template syntax
• Conditional string rendering with support for nested expressions
• Variable (interpolation / subsitution / expansion) with support for property accessor chaining
• Parse/compile your templates once, execute them multiple times with different values
• Support for array output, allowing substitution of non-string values (such as React components)
• Extensible with custom functions (or use our Standard Library (fns))
• Bundle-bloat friendly. Small, tree-shakeable library with zero dependencies
• Built with TypeScript, exports type definitions

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Documentation

Documentation and a demo are available at https://runty.js.org

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Installation

Install locally

NPM

npm install runty

Yarn

yarn add runty

Use via CDN

Unpkg

import { runty } from 'https://unpkg.com/runty/dist/index.mjs';

Skypack

import { runty } from 'https://cdn.skypack.dev/runty';

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Quick Examples

Below are some quick examples demonstrating how runty can be used.

Simple Interpolations

The most basic usage of runty is to interpolate values from an object into a string:

import { runty } from 'runty';

// parse a string template
const template = runty.string('Hello {%name}!');

// execute a template and pass it a dictionary of variables
console.log(template({ name: 'Somebody' }));
// "Hello Somebody!"

// variable accessors can also access nested properties
const anotherTemplate = runty.string('Hello {%person.name}!');

console.log(template({ person: { name: 'Somebody' } }));
// "Hello Somebody!"

Conditional Interpolations

Runty also supports conditional expressions, which look similar to tenary syntax:

import { runty } from 'runty';

const template = runty.string('Good {%pm?night:morning}!');

console.log(template({ pm: false }));
// "Good morning!"

console.log(template({ pm: true }));
// "Good night!"

The else case is optional and will default to an empty string. Conditional interpolations can also have other interpolations nested inside of their if/else cases.

This example only renders the artist name and extra hyphen if an artist name is defined with a renderable value:

import { runty } from 'runty';

const template = runty.string('Now Playing: {%artist?{%artist} - }{%song}');

console.log(template({ artist: 'Weird Al Yankovic', song: 'Albuquerque' }));
// "Now Playing: Weird Al Yankovic - Albuquerque"

console.log(template({ song: 'Albuquerque' }));
// "Now Playing: Albuquerque"

Using Functions

Templates may also call functions, which can be enabled by Functions can be called from within templates, if enabled. One of the configurable options runty accepts is fns, an object of functions to make available to templates.

This example uses standard library fns, an optional collection of common logical, formatting, and data manipulation utilities which come with runty.

import { runty, fns } from 'runty';

// pass 'fns' option to runty
const template = runty.string(
  '{$gt(%count,0)?There {$eq(%count,1)?is:are} {%count} item{$not($eq(%count,1))?s} in your cart:Your cart is empty}.', 
  { fns }
);

console.log(template({ count: 0 }));
// "Your cart is empty."

console.log(template({ count: 1 }));
// "There is 1 item in your cart."

console.log(template({ count: 2 }));
// "There are 2 items in your cart."

Extending With Custom Functions

This example defines it's own custom functions:

import { runty } from 'runty';

// runty functions recieve two arguments:
// - a list of arguments passed by the template
// - a reference to the variable dictionary
const fns: {
  plural: ([num]) => Number(num) !== 1,
  fooOrBar: ([defaultValue], { bar, foo }) => bar ?? foo ?? defaultValue
};

const template = runty.string(
  'There {$plural(%count)?are:is} {%count} item{$plural(%count)?s} in your cart.',
  { fns }
);

console.log(template({ count: 1 }));
// "There is 1 item in your cart."

console.log(template({ count: 3 }));
// "There are 3 items in your cart."


const anotherTemplate = runty.string('This is {$fooOrBar(neither)}.', { fns });

console.log(anotherTemplate({ foo: 'Foo' }));
// "This is Foo."

console.log(anotherTemplate({ bar: 'Bar' }));
// "This is Bar."

console.log(anotherTemplate());
// "This is neither."

Getting Template Result As An Array

In some cases, it may be useful to interpolate non-stringifiable values in a string template.

For example, you might want to drop a React component into your template:

import React from 'react';
import { runty } from 'runty';

// compile an array template:
const template = runty.array('Drop a react component {%component} into your template.');

const Component = () => {
  const values = template({ component: <button key="foo" /> });

  return (
    <div>
      {values}
      // renders: ['Drop a react component ', <button key="foo" />, ' into your template.']
    </div>
  );
};

You can even create custom functions that return React components:

import React from 'react';
import { runty } from 'runty';
import { Link } from 'react-router-dom';

const fns = {
  link: ([label, path]) => (<Link key={`${label}-${path}`} to={path}>{label}</Link>)
};

const template = runty.array('You can {$link(Click here,/some/path)} to learn more.', { fns });

const Component = () => {
  const values = template();

  return (
    <div>
      {values}
      // renders: [
      //   'You can ',
      //   <Link key="Click here-/some/path" to="/some/path">Click here</Link>,
      //   ' into your template.'
      // ]
    </div>
  );
};