Map over object values and JSON parse
The very first concern is what if item just happens to be a string starting with [ or {? 

How about instead of testing for [ and {, why not try parsing it? And if it fails, just return as is? This way, you don't need half-hearted checks.

export function resolveValues (data) {
  return mapValues(data, item =&gt; {
    try{ return JSON.parse(item) }
    catch (e) { return item; };
  })
}