khan_interview: A JavaScript repository from wangfowen

#Challenge Framework#

Test out the framework at http://wangfowen.github.io/khan_interview

Write your tests in Advanced Unit Test. The tests will check the code in Student Code. Student Code is parsed by Acorn (reasoning explained further down in documentation) and wrapped in a Code object, reference-able within Advanced Unit Test via the variable code. Right now you can only run one test case at a time in Advanced Unit Test. test() has already been appended to the end of what you enter into the box for niceness. Test Result should reflect that test().

##Framework API##

Code(ast) - ast is an abstract syntax tree as specified by the Mozilla parser API (can be output by both Acorn and Esprima). Creates a Code object upon which you find all the other methods below
mustContain(type) - type is a string which matches one of the Node object types found in the Mozilla parser API. Tests to see if the Node object of type type is within the AST array of the Code object - essentially a whitelist of functionality. Returns a Code object with the children of the type Node as the AST array. Empty AST array if not found.
```
code.mustContain("ForStatement");
code.mustContain("VariableDeclaration");
```
is equivalent to "This program MUST use a 'for loop' and a 'variable declaration'."
mustNotContain(type) - same situation as mustContain, except returns the same Code object if the Node is not in the AST and returns empty array if it is. Used to test for a blacklist of functionality.
```
code.mustNotContain("WhileStatement");
code.mustNotContain("IfStatement");
```
is equivalent to "This program MUST NOT use a 'while loop' or an 'if statement'."
whichMustContain(type) - an alias for mustContain. Sounds better when you're chaining to determine the rough structure of a program.
```
code.mustContain("ForStatement")
    .whichMustContain("IfStatement");
```
is equivalent to
```
var forStatement = code.mustContain("ForStatement");
forStatement.mustContain("IfStatement");
```
which is equivalent to "There should be a 'for loop' and inside of it there should be an 'if statement'."
whichMustNotContain(type) - an alias for mustNotContain.
test() - returns a boolean of whether the AST object is empty or not. Stick it at the end of your other statements to easily see whether your tests passed or not.
```
code.mustContain("ForStatement")
    .whichMustContain("IfStatement")
    .test();
```

##Improvements To Make##

Given more time, I'd add some security checks to make sure the students aren't abusing the Advanced Unit Test console. I'd drop the eval since that's dangerous and parse the input instead to see which methods to be running.

I'd also either rename the methods or change the way they work so that it makes more sense. mustContain suggests it'd return a boolean, but it doesn't unless you append the test().

Additionally, it'd be neat if it could test multiple conditions at once, stylistically the way d3 chains. For example:

code.mustContain("ForStatement")
      .whichMustContain("IfStatement")
    .andMustContain("WhileStatement")
      .whichMustContain("VariableDeclaration")
    .test();

##Acorn vs Esprima##

Acorn is 72% the size of Esprima (not minified).
Both support ECMAScript 5. Esprima only partly supports 6.
Acorn supports IE5 and on. Esprima only supports modern browsers.
Acorn's continuous integration has 800+ test cases. Esprima has 900+ test cases and has better documentation about its test coverage and performance.
Both are well documented enough to be easily used. Looking at them as black boxes, both have the same base input and output. Acorn has more optional inputs for customization.
For performance comparison (ironically provided by Esprima), Acorn performed better for parsing smaller Javascript libraries. It didn't perform as well for large libraries like JQuery, but it's unlikely students' code would become so verbose.

The main goals in my choosing a parser is ease of use as a developer and speed for the end user. For the first goal, both libraries are adequate. For the second, Acorn is better, thus that was the library I ended up going with for my test setup.

wangfowen/khan_interview