7.1 Type Conversion https://tc39.github.io/ecma262/#sec-type-conversion 7.1.1 ToPrimitive(input [, PreferredType]) https://tc39.github.io/ecma262/#sec-toprimitive
function ToPrimitive(input, PreferredType) {
            switch (Type(input)) {
                case 0 /* Undefined */: return input;
                case 1 /* Null */: return input;
                case 2 /* Boolean */: return input;
                case 3 /* String */: return input;
                case 4 /* Symbol */: return input;
                case 5 /* Number */: return input;
            }
            var hint = PreferredType === 3 /* String */ ? "string" : PreferredType === 5 /* Number */ ? "number" : "default";
            var exoticToPrim = GetMethod(input, toPrimitiveSymbol);
            if (exoticToPrim !== undefined) {
                var result = exoticToPrim.call(input, hint);
                if (IsObject(result))
                    throw new TypeError();
                return result;
            }
            return OrdinaryToPrimitive(input, hint === "default" ? "number" : hint);
        }