skelt

Skelt is a templating engine for object literals.

• Installation
• Usage
• Performance
• Contributing

Installation

Install with:

npm install -S skelt

or

yarn add skelt

Usage

When you need to build complex JS objects dynamically from a predefined template object, use Skelt to benefit from testability capabilities.

Skelt is a deadly simple function: the first argument represent your template object, whereas the second argument is a parameters object with all values required by the template.

skelt = (template, parameters) => object

Here is the compulsory "hello, world" example:

import skelt from 'skelt';

const template = {
    welcome: ({ name }) => `Hello ${name}`
};

skelt(template, { name: 'world' });
// {
//    welcome: 'Hello world'
// }

At build step, the template is walked and resolved recursively. That means that all functions values are executed with the parameters object as argument. Non-function values are just passed as is.

import skelt from 'skelt';

const personTemplate = {
    fullName: ({firstName, lastName }) => `${firstName} ${lastName}`,
    age: ({ age }) => age,
    misc: {
        isAdult: ({ age }) => age > 21,
    }
};

skelt(personTemplate, { firstName: 'John', lastName: 'Doe', age: 42 });
// {
//    fullName: 'John Doe',
//    age: 42,
//    misc: {
//        isAdult: true,
//    },
// }

The template can also be a function returning an object, which somehow makes writing templates easier:

import skelt from 'skelt';

const isAdult = ({ age }) => age > 21;

const personTemplate = ({ age, firstName, lastName }) => ({
    fullName: `${firstName} ${lastName}`,
    age,
    misc: {
        isAdult,
    }
});

skelt(personTemplate, { lastname: 'John', firstname: 'Doe', age: 42 });

// same result as above

That means you can build very complex objects from simple templates using composition, as shown in the example below.

import skelt from 'skelt';

const url = ({ locale }) => `http://www.example.com/${locale}`;
const localize = choices => ({ locale }) => choices[locale]; // higher-order function!
const title = localize({
    fr: 'Bienvenue sur mon site',
    en: 'Welcome on my website',
});

const homeTemplate = {
    url,
    title,
    body: localize({
        fr: 'Bonjour le monde',
        de: 'Hello, world',
    }),
    tags: localize({
        fr: ['accueil', 'test'],
        en: ['welcome', 'test'],
    })
};

skelt(homeTemplate, { locale: 'fr' });
// {
//    url: 'http://www.example.com/fr',
//    title: 'Bienvenue sur mon site',
//    body: 'Bonjour le monde',
//    tags: ['accueil', 'test'],
// }

Use Memoize To Improve Performance

Because of the full traversal and resolving of the template, performance can sometimes be suboptimal.

To speed up the computing time for templating, you can use the memoize function of your choice in your template. This way, functions are only called the first time the template is rendered. Here is an example:

import skelt from 'skelt';
import memoize from 'lodash/memoize';

import fibonnaci from './some-fibonnaci-module';

skelt({
    function: 'fibonnaci',
    result: memoize(fibonnaci),
}, { n: 10 });

// {
//    function: 'fibonnaci',
//    result: 55, // computed only the first time for n = 10
// }

Contributing

Run the tests with this command:

make test

License

Skelt is licensed under the MIT Licence, courtesy of Marmelab and ARTE.