felixarntz/theme-boilerplate

/**
 * File skip-link-focus-fix.js.
 *
 * Helps with accessibility for keyboard only users.
 *
 * Learn more: https://git.io/vWdr2
 */

function detectUserAgent() {
    const userAgents = [ 'webkit', 'opera', 'msie' ];
    let userAgent;

    for ( userAgent of userAgents ) {
        if ( navigator.userAgent.toLowerCase().indexOf( userAgent ) > -1 ) {
            return userAgent;
        }
    }

    return '';
}

class SkipLinkFocusFix {
    constructor() {
        this.userAgent = detectUserAgent();
    }

    initialize() {
        if ( ! this.userAgent.length ) {
            return;
        }

        if ( ! document.getElementById || ! window.addEventListener ) {
            return;
        }

        window.addEventListener( 'hashchange', function() {
            var id = location.hash.substring( 1 ),
                element;

            if ( ! ( /^[A-z0-9_-]+$/.test( id ) ) ) {
                return;
            }

            element = document.getElementById( id );

            if ( element ) {
                if ( ! ( /^(?:a|select|input|button|textarea)$/i.test( element.tagName ) ) ) {
                    element.tabIndex = -1;
                }

                element.focus();
            }
        }, false );
    }
}

export default SkipLinkFocusFix;