javascript - Change data-percentage attribute everyday -

i'm trying change data-percenatage attribute of element 6 everyday, it's not working or i'm doing wrong. can take , tell me wrong? have few elements data percentage , want change them everyday.

$(document).ready(function() {     var dzisiaj = new date();     var dzien = dzisiaj.getday();     if(dzien==0)     {         var dana = $("#l1").data-percent();         dana = dana + 6;         $("#l1").attr("data-percent", dana);     }     else if(dzien==1)     {         var dana = $("#l1").data-percent();         dana = dana + 6;         $("#l1").attr("data-percent", dana);     }     else if(dzien==2)     {         var dana = $("#l1").data-percent();         dana = dana + 6;         $("#l1").attr("data-percent", dana);     }     else if(dzien==3)     {         var dana = $("#l1").data-percent();         dana = dana + 6;         $("#l1").attr("data-percent", dana);     }     else if(dzien==4)     {         var dana = $("#l1").data-percent();         dana = dana + 6;         $("#l1").attr("data-percent", dana);     }     else if(dzien==5)     {         var dana = $("#l1").data-percent();         dana = dana + 6;         $("#l1").attr("data-percent", dana);     }     else if(dzien==6)     {         var dana = $("#l1").data-percent();         dana = dana + 6;         $("#l1").attr("data-percent", dana);     } }); 

here element in html

<span id="l1" class="chart" data-percent="300"> <span class="percent"></span> </span> 

there multiple problems in code

1. reading attribute data-percent wrong, reading teh data property value of jquery object(which not there) subtracting value returned percent method(which i'm guessing not there resulting in error)
2. the attribute value string, need convert nemeric addition so

try

var dzisiaj = new date(); var dzien = dzisiaj.getday();  var dana = +$("#l1").attr('data-percent') || 0; dana += 6; $("#l1").attr("data-percent", dana);