Naplnění this.pole z JONSu

class Media{
    constructor(media, path, id){
        this.medium = media;
        this.path = path;
        this.content = this.medium.nodeName.toLowerCase();
        this.extent = this.content=="audio" ? ".mp3" : ".mp4";
        
        this.pole = new Array();
        test  = new Array();
        $.getJSON( path+"/metadata/sync-"+ this.content +".json", function( data){
            $.each( data, function( key, val ){
                test.push( key);
                 this.pole.push( key);    // vypíše Uncaught TypeError: this.pole is undefined
            })
        });
    });
}