Why is my callback not a typeof function?

Question

var arr = [1,4,5];
var getMaxOfArray = function(list, callback) { //this function return the max
    if (typeof callback === "function")
        return Math.max.apply(Math, callback.call(list));
    else 
        return -1;
};

var cb = function(list) { //callback adds two to each value to a new array
    var results = [];
    for (var i=0; i<list.length; i++) {
        results.push(list[i] + 2);
    }  
    return results;
};


//cb(arr);

getMaxOfArray(arr, cb(arr));

When I call cb(arr), it evaluates as a function and returns the expected outcome of [3,6,7], but when I try to call getMaxOfArray(arr, cb(arr)); my conditional returns -1, showing that it is not a function? What am I doing wrong?

Answer 1

first, u need to call the getMaxOfArray method like this:

getMaxOfArray(arr, cb);

second, change the calling line to this:

return Math.max.apply(Math, callback.call(this, list));

or simply call the callback:

return Math.max.apply(Math, callback(list));