ConstValue is a plain object, created using typical {object: "notation"} or an object with no prototype ({__proto__:null} or Object.create(null)). Functions, Dates, Maps, Sets, Errors, RegExps, arrays and libraries like Math are not considered plain, nor are objects that have tampered with [Symbol.toStringTag].
Alias of isPlainObject. Stands for "is plain old JavaScript object".