WP Post Preview link

gistfile1.php

// credit: https://wordpress.stackexchange.com/questions/191918/custom-post-preview-without-saving
// related: https://support.advancedcustomfields.com/forums/topic/preview-solution/

add_filter( 'preview_post_link', function ( $link ) {
    return 'http://domain.com/mobile-preview/?src=' . urlencode($link) . '%26admin_bar=false';
} );

--

(function ($) {

    $(document).ready(function () {

        // Create URL for post preview
        var previewUrl = $('#preview-action').find('.preview').attr('href');
        var parser = document.createElement('a');
        parser.href = previewUrl;
        var postId = $('#post_ID').val();
        mobilePreviewUrl = parser.protocol + '//' + parser.host + '?p=' + postId;

        var href = mobilePreviewUrl ? 'http://domain.com/mobile-preview/?src=' + encodeURIComponent(mobilePreviewUrl) + '%26preview=true' : '';

        // Preview buttons
        var mobilePreviewBtn = $('<a/>').addClass('preview button').attr({
            'id'    : 'mobile-preview',
            'href'  : href,
            'target': '_new'
        }).text('Preview Mobile');
        $('#preview-action').prepend(mobilePreviewBtn);
        $('#post-preview').hide();
        mobilePreviewBtn.on('click', function(e){
            e.preventDefault();
            $(window).off( 'beforeunload.edit-post' );
            wp.autosave.server.tempBlockSave();
            $('form#post').submit();
            window.open(href, 'mobilePreview');
        });

    }); // end document ready

})(jQuery);