js objects and iterators problem set

Author: nathanallen

Diff for: README.md

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+# <img src="https://cloud.githubusercontent.com/assets/7833470/10899314/63829980-8188-11e5-8cdd-4ded5bcb6e36.png" height="60"> Javascript Objects - Problem Set
+
+* Please **Fork & Clone** this repo.
+* For each problem, modify the relevant file in the `challenges`folder. We encourage you to *commit often* and push your changes to github.
+* You will [submit this problem set for review](https://github.com/SF-WDI-LABS/shared_modules/blob/master/how-to/submit-homework.md).
+
+## Challenges
+1. [Letter Count](/challenges/letter-count.js)
+2. [Query String Parser](/challenges/query-string-parser.js)
+3. [Birthday Countdown](/challenges/birthday-countdown.js)
+4. [Ping Pong](/challenges/ping-pong.js)
+
+#### Key Concepts
+* Working with **key-value pairs**
+* Drilling into complex objects using **dot notation** and **bracket notation**
+* Dynamically setting keys in **objects** (i.e. keys are not hard-coded).
+* Using Array **iteration** methods.
+
+## Executing your code
+There are a number of options for running/executing your code. They all have their uses, so we encourage you to learn all of them:
+
+- From the browser:
+    - **Using the [Chrome Developer Console](https://developers.google.com/web/tools/chrome-devtools/debug/console/console-ui?hl=en#opening-the-console)**
+        * Tip: Use `↑` and `↓` to cycle through your code history. Pressing `→` selects the current suggestion. If there’s a single suggestion, `Tab` to select it.
+    + **Using [Javascript Snippets](https://developers.google.com/web/tools/chrome-devtools/debug/snippets/)** to execute and save your scripts.
+- From the command line:
+    + **Using the [Node REPL / Shell](http://www.nodelabs.org/repl.html)**
+        * Tip: Type `.exit` to quit. Use `↑` and `↓` to cycle through your code history.
+    + **Using the [`node some-file.js` command](http://javascript.cs.lmu.edu/notes/commandlinejs/)**
+        * Tip: Use `ctrl` + `c` (shortcut) to quit "hanging" programs. And make sure to `console.log("your output")`.

Diff for: challenges/birthday-countdown.js

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+/*
+
+  Create a function `daysUntilDate` that accepts a string (with the format `"mm/dd/yyyy"`) and
+  returns the number of days (integer) between today and that date. Please use the built in
+  Javascript `Date` type in your solution.
+
+  See: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date
+
+  Next, create a function `birthdayReminder` that accepts an array of objects, containing a person's
+  date of birth (dob), and returns an array of reminder messages (strings).
+
+  ```javascript
+  birthdayReminder([
+    {
+      name: "Jack",
+      dob: "10/31/2013"
+    },
+    {
+      name: "Jill",
+      dob: "4/01/1975"
+    }
+  ]);
+
+  //=> [
+  //      "Jack's birthday is in 75 days",
+  //      "Jill's birthday is in 305 days"
+  //    ]
+  ```
+
+  Bonuses
+  - Will your function still work tomorrow when the date is different? Is it future proofed?
+  - To make your output more relevant, can you sort by days remaining (ascending)?
+
+*/
+
+// YOUR CODE HERE

Diff for: challenges/letter-count.js

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+/*
+
+  Create a function `letterCount` that accepts a string, and finds the number of times each letter
+  occurs in the string. For example, given the word "apple", letterCount("apple") should count all
+  occurrences of the letters "a", "p", "l" and "e" and then return the following output:
+
+  ```javascript
+  {
+    "a": 1,
+    "p": 2,
+    "l": 1,
+    "e": 1
+  }
+  ```
+
+  Bonuses
+  - Make sure that lower case letters and upper case letters count for the same character.
+  - Ignore spaces, special characters, and punctuation.
+  - Instead of just counting letters, calculate their percent-based frequency.
+    See: http://www.math.cornell.edu/~mec/2003-2004/cryptography/subs/frequencies.html
+
+    ```javascript
+    {
+      "a": 0.2, // percent
+      "p": 0.4,
+      "l": 0.2,
+      "e": 0.2
+    }
+    ```
+
+*/
+
+// YOUR CODE HERE

Diff for: challenges/ping-pong.js

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+/*
+
+  In this challenge you will simulate the movement of a ping-pong, bouncing back and forth across a
+  table.
+
+  Create a function `pingPong` that accepts an array, and returns the *same* array
+  with the ping-pong moved one cell. Each time the ping-pong moves, you must increment the
+  ping-pong's `steps` counter by 1. The direction of movement should be determined soley by the
+  current state of the array and the current `steps` value of the ping-pong.
+
+  ``` javascript
+  var table = [{steps: 0}, null, null, null];
+
+  pingPong(table); //=> [null, {steps: 1}, null, null]
+  pingPong(table); //=> [null, null, {steps: 2}, null]
+  pingPong(table); //=> [null, null, null, {steps: 3}]
+  pingPong(table); //=> [null, null, {steps: 4}, null]
+  pingPong(table); //=> [null, {steps: 5}, null, null]
+  pingPong(table); //=> [{steps: 6}, null, null, null]
+  pingPong(table); //=> [null, {steps: 7}, null, null]
+
+  table; //=> [null, {steps: 7}, null, null]
+  ```
+
+  Keep in mind that I should be able start this process at *any* point:
+
+  ```
+  var table = [null, {steps: 13}, null, null];
+  pingPong(table); //=> [null, null, {steps: 14}, null]
+  ```
+
+  Bonuses
+  - Allow arrays of *any length*
+  - We can think of the ping-pong as having an internal "speed" of 1. Allow this value to be
+    explicity set at a higher number (i.e. move 2 cells at a time, or 3 cells at a time).
+  - Support multiple ping-pongs.
+
+*/
+
+// YOUR CODE HERE

Diff for: challenges/query-string-parser.js

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+/*
+
+  Create a function `parseQueryString` that accepts a query string parameter as an argument, and
+  converts it into an object, using the following rules:
+
+    * An equals sign (`=`) separates a *key* on the left from a *value* on the right.
+    * An ampersand (`&`) separates key-value pairs from each other.
+    * All keys and values should be parsed as Strings.
+    * The query string will not contain spaces.
+
+  Here are some example inputs and outputs (mind the edge cases!):
+
+  ```javascript
+  parseQueryString("");
+  //=> {}
+
+  parseQueryString("a=1");
+  //=> {
+  //    "a": "1",
+  //   }
+
+  parseQueryString("first=alpha&last=omega");
+  //=> {
+  //    "first": "alpha",
+  //    "last": "omega"
+  //   }
+
+  parseQueryString("a=apple&b=beet&b=blueberry&c=&d=10");
+  //=> {
+  //    "a": "apple",
+  //    "b": "blueberry",   // "blueberry" overwrites "beet"!
+  //    "c": "",            // empty string (missing value)
+  //    "d": "10"           // "10" is a String!
+  //   }
+  ```
+
+  Mega Bonus
+  - Can you create the reverse function? Given an object, output a Query Parameter String:
+
+    ``` javascript
+    var o = {first: "alpha", last: "omega"};
+    convertToQueryParameter(o); // "first=alpha&last=omega";
+    ```
+
+*/
+
+// YOUR CODE HERE