Javascript interview question.

gistfile1.js

/**
 * Takes in an array of two objects, flattens the currArray, and prints an HTML Table of the values.
 * The HTML table has a column header which is a superset of all keys in all the objects.
 * Any values that have changed (ie field value changed or is a new key altogether) should be bolded.
 *
 * @param prevArray is an array of objects
 * @param currArray is an array of objects
 * @return a string with HTML markup in it, should return null if error occurs.
 */
function arrayDiffToHtmlTable( prevArray, currArray) {

    // Note: you cannot depend solely on array index for comparison.
    // The currArray could have more or potentially even be in a different order.
    // However, you can assume that each item in the arrays will have an "_id" parameter
    //
    // Example, Given the following data set:
    //
    //        var prevArray = [ {_id:1, someKey: "RINGING", meta: { subKey1: 1234, subKey2: 52 } } ];
    //        var currArray = [ {_id:1, someKey: "HANGUP",  meta: { subKey1: 1234, subKey2: 56 } },
    //            {_id:2, someKey: "RINGING", meta: { subKey1: 5678, subKey2: 207, subKey3: 52 } } ];
    //
    //        console.log( arrayDiffToHtmlTable( prevArray, currArray));
    //
    //  OUTPUT (Note this is a text representation... output should be an HTML table):
    //
    //          _id               someKey          meta_subKey1        meta_subKey2        meta_subKey3
    //            1              **HANGUP**             1234               **56**
    //          **2**            **RINGING**          **5678**             **207**             **52**
    //
    //  ** implies this field should be bold or highlighted.
    //  !!! analyze the example carefully as it demonstrates expected cases that need to be handled. !!!
    //
}