callbackExercises.md

#Callback Exercises

1. Write a function, funcCaller, that takes a func (a function) and an arg (any data type). The function returns the func called with arg(as an argument).

2. Write a function, firstVal, that takes an array, arr, and a function, func, and calls func with the first index of the arr, the index # and the whole array.

3. Change firstVal to work not only with arrays but also objects. Since objects are not ordered, you can use any key-value pair on the object.

4. [Extra Credit] Write a function, once, (see: http://underscorejs.org/#once) that takes a function and returns a version of that function which can only be called once. [Hint: you need a closure] You probably don't want to be able to double charge someone's credit card. Here is an example of how to use it:

  var chargeCreditCard = function(num, price){
    //charges credit card for a certain price
  };
  var processPaymentOnce = once(chargeCreditCard);
  processPaymentOnce(123456789012, 200);