In C#, there's expression trees which handle things like this and it's how Entity Framework is able to convert the lambdas it's given into SQL. This means that you can pass around code that can be inspected or transformed instead of being executed. Take this EntityFramework snippet:

    db.People.Where(p => p.Name == "Joe")

`Where` takes an `Expression<Func<T, bool>> predicate`. It isn't taking the `Func` itself, but an `Expression` of it so that it can look at the code rather than execute it. It can see that it's trying to match the `Name` field to the value "Joe" and translate that into a SQL WHERE clause.

Since JS doesn't have this, they have to pass in a special placeholder value and try to record what the code is doing to that value.