How can I add custom key/values on the fly in my script?

(function ( $ ) {


$.fn.dropDown = function(props) {

/***********************

'props' is the object passed to the function call. You can then create multiple key/value pairs. 

In this case, we have the parent of the dropdown, the dropdown content, and the close/open text, which will be 
appended to the aria-label

************************/

var element = this;
   // set atts for element
    $(element).attr({
      "tabindex": "0", 
      "role": "button",
      "aria-expanded": "false",
      "aria-pressed": "false",
      "data-closed-text": props.closedText,
      "data-open-text": props.openText,
      "aria-label": props.closedText
    });

    // set content to be focusable on keyboard
    $(element).next(props.dropdown).attr({
      "tabindex": "0"
    });


  // set above atts on click, keypress events
  $(element).on('click keypress', function() {
      if((element).attr('aria-pressed') === "false") {
        $(element).attr({
          'aria-pressed': 'true',
          'aria-expanded': 'true',
          'aria-label': props.openText
        });
        $(element).parents(props.parent).find(props.dropdown).css('height', "400px");
      } else {
        $(element).attr({
          'aria-pressed': 'false',
          'aria-expanded': 'false',
          'aria-label': props.closedText
        });
        $(element).parents(props.parent).find(props.dropdown).css('height', "");
      }
  });

};


}( jQuery ));

$('.container').dropDown({
    "closedText": "drop-down collapsed", // define closed text for aria-label
    "openText": "drop-down expanded", // define open text for aria-label
    "parent": ".book-now", // select parent container for context
    "dropdown": ".content" // select dropdown element 


});