JSFiddle - React, Tailwind, and code Playground

JavaScript

var mainobj={
  "2009-01": {
    "bbcfour": 324,
    "bbcnews24": 1075,
    "bbcone": 940,
    "bbcthree": 441,
    "bbctwo": 1040,
    "cbbc": 898,
    "cbeebies": 1343
  },
  "2009-02": {
    "bbcfour": 295,
    "bbcnews24": 958,
    "bbcone": 904,
    "bbcthree": 434,
    "bbctwo": 1038,
    "cbbc": 793,
    "cbeebies": 1246
  }
};


var my2darray=[];

for (var date in mainobj) {
   var temparray=[date];
    for(val in mainobj[date]){
        temparray.push(mainobj[date][val]);
    }
   my2darray.push(temparray);
}
console.log(my2darray);