Underpants

This activity is essentially a re-write of underscore.js.

Why?

In the past exercises we've been writing a lot of loops over objects and arrays ourselves. Instead of doing that, we are going to write several fuctions to handle the looping for us. These functions are used every day by professional developers and we're well on our way to becoming professional developers!!

This means that if we're confused about how a function should work, we can check the underscore.js documentation linked above for help.

Instructions

• Open up index.html in a web browser.
• Notice that all the tests are failing. :)
• Open up underpants.js in a text editor and follow the instructions.
• Make all the test pass!!
• Open underpants.html in a text editor to view the code that runs the tests.

Links and Resources

Some quick notes that may come in handy:

• underscore documentation.
• Many of the functions operate on "collections." They can take both arrays or objects as their arguments and you need to be able to handle both cases.
  • You can use Array.isArray(obj) to find out whether an object is an array.
  • You can use obj.length to test if something is either a string or an array.
• Javascript has a built-in Math object that provides some very useful functions. Math Documentation.
• Within a function, you can use the arguments variable to access all the parameters that were passed in even if they aren't named in the function definition. This is useful if you don't know how many arguments are going to be passed in in advance.
  • You can count the arguments by using arguments.length and access each argument using arguments[i].
  • The arguments object is very similar to an array, but note that it does not support most array functions (such as slice or push). You can read more about this here.

Extra Credit:

See Instructor for instructions.

• defaults
• once
• memoize
• delay
• shuffle

Double Extra Credit:

See Instructor for instructions.

• once
• invoke
• sortBy
• zip
• flatten
• intersection
• difference
• throttle

Note: Some browsers provide built-in functions--including forEach, map, reduce and filter--that replicate the functionality of some of the functions you will implement. Don't use them to implement your functions.