Need documentation on "opendatakit" JS Object API

What is the problem? Please be detailed.
I’ve been using ODK1.x and have decided to switch to ODK2.0 because I’m excited for some of the features I read about.

In the latest documentation I could find (i.e. Rev208 documentation), the docs mention that we have access to a opendatakit JS object in two areas:

  1. The calculate column in the ‘survey’ sheet
  2. The ‘calculates’ sheet

Where can I find the latest documentation on what functions are supported by the opendatakit JS object? I’m looking for something similar to ODK1’s join(delimiter, nodeset) or join(delimiter, variable-number-of-strings)

A followup, sanity question I have is, is the rev208 documentation on how to write the XSLX forms the latest available? I don’t want to miss out on any gotchas or other new features.

What ODK tool and version are you using? And on what device and operating system version?
ODK2.0 Rev210 RC1, Win10 & Android

The 210 documentation is not yet available on the user site (we are in the grindingly-slow process of converting that site to drupal).

The 208 documentation is generally accurate, though there have been changes in the XLSX content, most notably the changes to the display… columns on the survey, choices and settings sheets. These are now display.prompt.text, display.hint.text, display.title.text, and display.prompt.image, etc. These changes were made to enable better support for translations. The exampleForm shows a trivial use of translations. Translations for the strings displayed in the built-in widgets are provided via the framework form.

At the internals and web-programmer level, the up-to-date documentation is here:

In answer to your question, there is no join function. However, the full power of javascript and the jquery.js ($.xxx) and underscore.js ( libraries are available to you. The calculate column is wrapped and evaluated as a javascript function:

function() {

You can write your own code to perform a join via defining and invoking an anonymous function in your calculate. Here is an example:

(function() { 
     var result = ""; 
     _.each(data('valueListField'), function(element) { 
            result = result + ", " + element; 
     return result.substring(2); 
  }) ()

This defines a function and then invokes it. The available accessor functions within a calculates expression are the following:

    data(fieldName)  -- retrieve the value stored under this fieldName
          Usage: data('myField')

    metadata(instanceMetadataFieldName) -- retrieve value stored under this name
          Usage: metadata('_group_modify')

    selected(promptValue, qValue) -- test whether qValue occurs within a select-multiple
                Usage:  selected(data('mySelectMultipleField'),'myChoiceDataValue')

    countSelected(promptValue) -- count the number of selections in a select-multiple
                Usage: countSelected(data('mySelectMultipleField'))

    equivalent(promptValue1, promptValue2, ...) -- test if values are equivalent
                Usage: equivalent(data('promptA'), data('promptB'))

    not(conditional) -- negate a condition ( equivalent to !(conditional) )
                 Usage: not(data('fieldA') === data('fieldB'))

now() -- return the current time

    isFinalized() -- return whether or not the current row is finalized

    assign(fieldName, value) -- store value in fieldName and return value.
               Usage: (8 + assign('myField', 5))*10

These formulas are also available, but are generally not useful in calculates. They are used within template helper functions (…/system/survey/js/handlebarsHelpers.js).

getCurrentLocale() -- return the currently-active locale

    localize(locale, displayProperty)  -- localize the given text
               Usage: localize(getCurrentLocale(), display.hint)

    width(string) -- determine the rendered width of a string

expandFormDirRelativeUrlPath(content) -- return url for a file within the form directory. 

Additionally, you can also reference the opendatakit object within these functions (system/survey/js/opendatakit.js).

Thank you for your very detailed post! So to summarize, all the following calls/objects are legal/available in the calculates section/calculation column in the xlsxform for ODK 2.0:

$.some_func() (jQuery Functions)
_.some_func() (underscore.js libraries)
handlebarsHelpers.one_of_the_functions_listed_above() (but you mentioned these functions are probably not useful)
opendatakit.some_func() (the opendatakit JS object API, the code of which can be found in the app-designer directory: system/survey/js/opendatakit.js)