Find the most frequent item of an array

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1

var arr1=[3, ‘a’, ‘a’, ‘a’, 2, 3, ‘a’, 3, ‘a’, 2, 4, 9, 3];
var mf = 1;
var m = 0;
var item;
for (var i=0; i<arr1.length; i++)
{

       for (var j=i; j<arr1.length; j++)
        {
                if (arr1[i] == arr1[j])
                 m++;
                if (mf<m)
                {
                  mf=m; 
                  item = arr1[i];
                }
        }
        m=0;

}
console.log(item+" ( " +mf +" times ) ") ;

please someone help i cant understand the code with grey background