Use a proxy to inspect properties used in a JS object.

propertyInspectionProxy.ts

const propertyIsNumeric = (property): boolean => {
  if (typeof property === "number") return true;
  if (typeof property === "string" && property.match(/\d+/)) return true;
  return false;
};

const NON_PROXIED_PROPERTIES = new Set([
  "typedAttributes",
  "attributes",
  "_originalAttributes",
]);

const shouldProxyPropertyValue = (property): boolean =>
  !NON_PROXIED_PROPERTIES.has(property);

function propertyUsageInspectionProxy<T = unknown>(
  obj: T,
  labelPrefix = "",
  usedProperties = new Set<string | number | symbol>()
): [T, Set<string | number | symbol>] {
  if (obj === null || typeof obj !== "object") {
    return [obj, usedProperties];
  }

  const castedObj = obj as T & object;

  const proxy = new Proxy(castedObj, {
    get(obj, property): any {
      const propertyValue = obj[property];

      const propertyDescriptor = propertyIsNumeric(property)
        ? `[]`
        : String(property);

      const propertyLabel = `${labelPrefix}.${propertyDescriptor}`;

      if (typeof propertyValue !== "function")
        usedProperties.add(propertyLabel);

      if (!shouldProxyPropertyValue(property)) return propertyValue;

      const [potentiallyProxiedPropertyValue] = propertyUsageInspectionProxy(
        propertyValue,
        propertyLabel,
        usedProperties
      );

      return potentiallyProxiedPropertyValue;
    },
  });

  return [proxy, usedProperties];
}