lib/js/src/util/focustrap.js

/**
 * --------------------------------------------------------------------------
 * Bootstrap (v5.1.3): util/focustrap.js
 * Licensed under MIT (https://github.com/twbs/bootstrap/blob/main/LICENSE)
 * --------------------------------------------------------------------------
 */

import EventHandler from '../dom/event-handler'
import SelectorEngine from '../dom/selector-engine'
import {
    typeCheckConfig
} from './index'

const Default = {
    trapElement: null, // The element to trap focus inside of
    autofocus: true
}

const DefaultType = {
    trapElement: 'element',
    autofocus: 'boolean'
}

const NAME = 'focustrap'
const DATA_KEY = 'bs.focustrap'
const EVENT_KEY = `.${DATA_KEY}`
const EVENT_FOCUSIN = `focusin${EVENT_KEY}`
const EVENT_KEYDOWN_TAB = `keydown.tab${EVENT_KEY}`

const TAB_KEY = 'Tab'
const TAB_NAV_FORWARD = 'forward'
const TAB_NAV_BACKWARD = 'backward'

class FocusTrap {
    constructor(config) {
        this._config = this._getConfig(config)
        this._isActive = false
        this._lastTabNavDirection = null
    }

    activate() {
        const {
            trapElement,
            autofocus
        } = this._config

        if (this._isActive) {
            return
        }

        if (autofocus) {
            trapElement.focus()
        }

        EventHandler.off(document, EVENT_KEY) // guard against infinite focus loop
        EventHandler.on(document, EVENT_FOCUSIN, event => this._handleFocusin(event))
        EventHandler.on(document, EVENT_KEYDOWN_TAB, event => this._handleKeydown(event))

        this._isActive = true
    }

    deactivate() {
        if (!this._isActive) {
            return
        }

        this._isActive = false
        EventHandler.off(document, EVENT_KEY)
    }

    // Private

    _handleFocusin(event) {
        const {
            target
        } = event
        const {
            trapElement
        } = this._config

        if (target === document || target === trapElement || trapElement.contains(target)) {
            return
        }

        const elements = SelectorEngine.focusableChildren(trapElement)

        if (elements.length === 0) {
            trapElement.focus()
        } else if (this._lastTabNavDirection === TAB_NAV_BACKWARD) {
            elements[elements.length - 1].focus()
        } else {
            elements[0].focus()
        }
    }

    _handleKeydown(event) {
        if (event.key !== TAB_KEY) {
            return
        }

        this._lastTabNavDirection = event.shiftKey ? TAB_NAV_BACKWARD : TAB_NAV_FORWARD
    }

    _getConfig(config) {
        config = {
            ...Default,
            ...(typeof config === 'object' ? config : {})
        }
        typeCheckConfig(NAME, config, DefaultType)
        return config
    }
}

export default FocusTrap