Initial attempt

function maxMinAvg(arr) {
    var max = arr[0];
    var min = arr[0];
    var avg = 0;
    var arrnew = [max, min, avg];
    
    for(var a=0; a<arr.length; a++){
        if(arr[a]>max){
            max = arr[a];
        }
        if(arr[a]<min){
            min = arr[a];
        }
        avg = arr[a]+avg;
        avg = avg/arr.length;
    }
    return arrnew; 
}