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Design systems - customisation (app-specific)

When performing design system customisations, you can control the scope as follows:

  • General - applied to all applications using the system.
  • Application-specific - only applied to a single application. This is described below.

You can also choose to customise either all the components or only individual ones.

Customising all components​

When you register a design system in an application, there are several configuration options that affect all the components provided by that design system.

Prefix​

You can override the default prefix set in the _config folder for a specific application as follows:

import { alphaButton, provideDesignSystem } from '@genesislcap/alpha-design-system';

provideDesignSystem()
    .withPrefix('custom')
    .register(alphaButton())

The element can then be used in HTML using the custom prefix:

<custom-button>Button</custom-button>

Default shadow DOM mode​

You can override the default shadow root mode (typically open, as that is both recommended and the default). You can choose to close all shadow roots by default using withShadowRootMode():

provideDesignSystem()
    .withShadowRootMode('closed')
    .register(/* ... */)

Name disambiguation​

By default, an element registered with an already-taken name will not be re-registered with the platform. However, its element definition callback will still be invoked, allowing it to define an alternate presentation (styles and template), scoped to the DOM tree that the design system is defined on.

As a best practice, one should try to avoid registering the same component more than once. If your architecture makes this difficult or impossible, you can provide a custom callback to handle disambiguating the duplicate elements.

The ElementDisambiguationCallback will be passed the tag name being registered, the type being registered, and the type that was already registered with the tag. Your callback can then return one of three types of values:

  • string - return a string to select an different name for the element to be registered under.
  • ElementDisambiguation.definitionCallbackOnly - this is the default callback's return value, which prevents re-registering the element but allows its callback to run and define different presentations for the element (styles and template). Note that having more than one presentation for the same element will trigger a slower rendering code path for elements of that type. So, it's best to avoid this unless it's absolutely needed for your application design.
  • ElementDisambiguation.ignoreDuplicate - this option completely ignores the duplicate element; no action is taken during registration if an element with the same tag is already registered.

Here's an example custom disambiguation callback showing a couple of these options.

provideDesignSystem()
    .withElementDisambiguation((nameAttempt, typeAttempt, existingType) => {
        if (nameAttempt === "foo") {
            return "bar";
        }

        return ElementDisambiguation.ignoreDuplicate;
    })
    .register(/* ... */)

Customising individual components​

The APIs described above impact all components, but those options can also be configured or overridden on a per-component basis. Configuring the component itself takes priority over any design system configuration.

Prefix​

The prefix for a component can be configured for a component registration by providing a configuration object with a prefix field during registration:

provideDesignSystem()
    .register(
        alphaButton({ prefix: 'custom' })
    );

Template​

To use a custom template for a component, provide a template field to the configuration object during registration:

provideDesignSystem()
    .register(
        alphaButton({
            template: html`
                <p>A completely new template</p>
            `
        })
    )

Styles​

Styles for a component can be configured as well, by providing a styles field to the configuration object during registration:

provideDesignSystem()
    .register(
        alphaButton({
            styles: css`
                /* completely replace the original styles */
            `
        })
    )

You can also use this technique to extend the existing styles; call the style function to import the originals and compose those with new styles. Here's what that would look like:

provideDesignSystem()
    .register(
        alphaButton({
            styles: (ctx, def) => css`
                ${buttonStyles(ctx, def)}
                /* add your style augmentations here */
            `
        })
    )

Shadow options​

Shadow options can be configured as well, including both shadow root mode and focus delegation:

provideDesignSystem()
    .register(
        alphaButton({
            shadowOptions: {
                mode: 'closed',
                delegatesFocus: true
            }
        })
    );

For more information on shadow options, see Element.attachShadow().