map_each_function.html

var each = function(collection, callback) {
	if( Array.isArray(collection) ) {
		for( var i = 0; i < collection.length; i++ ) {
			collection[i] = callback( collection[i] );
		}
	} else {
		for( var prop in collection ) {
			collection[prop] = callback( collection[prop] );
		}
	}
};

var map = function(collection, callback) {
	// Create new array so that old array is preserved
	var result = [];
	
  	// Add elements from old array to new array
	for( var i = 0; i < collection.length; i++ ){
		result[i] = collection[i];
	}
	
	// Pass new array through "each" function
	each(result, callback );
	
	// Return the value of the new array
	return result;
};

var allottedMinutes = [15, 20, 32];

var double = function (num) {
  return num * 2;
};

var doubledAllottments = map(allottedMinutes, double);

console.log(doubledAllottments); // logs [30, 40, 64]