diagnose JSON.stringify failure

json-Stringify.js

/* jshint esversion:6, node:false, strict:implied */
/* global print, context */

function createPartialCopy(obj, partialPropertyList) {
  // create new "partial copy" with only a subset of properties
  return partialPropertyList.reduce(function(a, prop) {
    a[prop] = obj[prop];
    return a;
  }, {});
}

function serializeOnePart(obj) {
  // create new "sub object" with only the keys from part1
  try {
    return JSON.stringify(obj);
  }
  catch (exc1) {
    var props = Object.keys(obj);
    if (props.length > 1)  {
      print("stringify still broken within this subset: " + JSON.stringify(props));
      return false;
    }
    else {
      context.setVariable('json_stringify_status', 'broken toplevel property: ' +  props[0]);
      return 1; // terminate
    }
  }
}

function diagnoseStringify(obj) {
  var props = Object.keys(obj); // [ "message", "token",..... ]

  // split the list of toplevel properties
  var part1Props = props.slice(0, props.length / 2);
  var part2Props = props.slice(props.length / 2);

  // Now, create "partial copies" of the object, and
  // try to serialize each one. This will narrow the error.

  // first half of property set
  var part1 = createPartialCopy(obj, part1Props);
  var r1 = serializeOnePart(part1);
  if (r1 === false) {
    // recurse
    diagnoseStringify(part1);
  }

  // second half
  var part2 = createPartialCopy(obj, part2Props);
  var r2 = serializeOnePart(part2);
  if (r2 === false) {
    // recurse
    diagnoseStringify(part2);
  }
}

var payload = ....;

try {
  // in 90% of the cases, this succeeds
  var result = JSON.stringify(payload, null, 2);
  context.setVariable('json_stringify_status', 'success, first cycle.');
}
catch(exc1) {
  // Possibly a runtime permission error.
  // We may lose the log message here, but this will help diagnose.
  diagnoseStringify(payload);
}