Jquery $.fn variable scope

Question

I faced a problem. I wrote my jquery component like below:

(function ( $ ) {

$.fn.addSocialShare = function() {

    this.append(getButtonHTML());
    return this;
};

var getButtonHTML = function(){
    var html;
    $.get('myUrl', function(data){
        html = data; // data is defined, request ok
    })        
    return html;
}
})( jQuery );

The problem is that html variable is not defined when I return it. How I can fix it? Where is my mistake?