infamous/src/html/behaviors/DefaultBehaviors.js

A CSS3D/WebGL UI library.

import Class from 'lowclass'
import Mixin from '../../core/Mixin'

export default
Mixin(Base =>

    // TODO This is here for now. Make it an extension to
    // element-behaviors so that it can be applied to any element
    // generically.
    Class('DefaultBehaviors').extends( Base, ({ Super }) => ({

        static: {
            // override in subclasses
            defaultBehaviors: [],
        },

        constructor(...args) {
            // Use the constructor return value, because we assume Base must be
            // a HTML element class, in which case this is currently unavoidable
            // because lowclass currently uses ES5-style constructors. This may
            // change when lowclass has `class` syntax option.
            const self = Super(this).constructor(...args)

            // If no geometry or material behavior is detected, add default ones.
            //
            // Deferring to a microtask doesn't work here, we must defer to a
            // macrotask with setTimeout, so we can detect if the element has
            // initial behaviors, otherwise the element's initial attributes
            // haven't been added yet (this is how HTML engines work, see
            // https://github.com/whatwg/dom/issues/522).
            //
            // TODO: If we use setTimeout (macrotask) deferral anywhere (like we do
            // here), and maybe even with microtask deferral (f.e. Promise), maybe
            // we should have a single place that initiate this deferral so that
            // everything in the engine can hook into it. Otherwise if different
            // call sites use setTimeout, logic will be firing at random and in
            // different order.
            setTimeout( () => self._setDefaultBehaviorsIfNeeded(), 0 )

            return self
        },

        _setDefaultBehaviorsIfNeeded() {
            let defaultBehaviors = this.constructor.defaultBehaviors

            // do nothing if there's no defaults
            if (!defaultBehaviors) return
            if (Object.keys(defaultBehaviors).length == 0) return

            const initialBehaviorNames = Array.from( this.behaviors.keys() )

            // small optimization: if there are no initial behaviors and we
            // have default behaviors, just set the default behaviors.
            if ( initialBehaviorNames.length == 0 ) {

                // if not an array, then it's an object.
                if (! ( defaultBehaviors instanceof Array ) ) defaultBehaviors = Object.keys( defaultBehaviors )

                this.setAttribute( 'has', this.getAttribute( 'has' ) + ` ${defaultBehaviors.join(' ')}`)
            }

            // otherwise detect which default behavior(s) to add
            else {

                let behaviorNamesToAdd = ''

                // if defaultBehaviors is an array, use default logic to add
                // behaviors that aren't already added.
                if (defaultBehaviors instanceof Array) {
                    for (const defaultBehaviorName of defaultBehaviors) {

                        let hasBehavior = false

                        for ( const initialBehaviorName of initialBehaviorNames ) {
                            if ( defaultBehaviorName == initialBehaviorName ) {
                                hasBehavior = true
                                break
                            }
                        }

                        if (hasBehavior) continue
                        else {
                            // TODO programmatic API:
                            //this.behaviors.add('box-geometry')

                            // add a space in front of each name except the first
                            if ( behaviorNamesToAdd ) behaviorNamesToAdd += ' '

                            behaviorNamesToAdd += defaultBehaviorName
                        }
                    }
                }

                // if defaultBehaviors is an object, then behaviors are added
                // based on conditions.
                else if (typeof defaultBehaviors == 'object') {
                    const defaultBehaviorNames = Object.keys(defaultBehaviors)

                    for (const defaultBehaviorName of defaultBehaviorNames) {
                        const condition = defaultBehaviors[defaultBehaviorName]

                        if (
                            (typeof condition == 'function' && condition( initialBehaviorNames ) ) ||
                            (typeof condition != 'function' && condition )
                        ) {

                            // add a space in front of each name except the first
                            if ( behaviorNamesToAdd ) behaviorNamesToAdd += ' '

                            behaviorNamesToAdd += defaultBehaviorName

                        }

                    }
                }

                // add the needed behaviors all at once.
                if (behaviorNamesToAdd) {
                    let currentHasValue = this.getAttribute('has')

                    if (currentHasValue) currentHasValue += ' '

                    this.setAttribute( 'has', currentHasValue + behaviorNamesToAdd )
                }
            }

        },

    }))
)