Long story short, OP is conflating closures with lambdas.

A closure is a lambda that is closed over its free variables meaning that the variables which are not defined in the body of the function (variables that are not local or the formal arguments) are bound to what their values are in that lexical scope at the time they are constructed and do not change with the calling environment.

In javascript if I do:

    var x = 2;
    var f = function() {
       return x;
    }
    console.log(f())
    (function() {
      var x = 3;
      console.log(f());
    })();
    

It will print '2' and '2'. f is a closure. It is closed over its free variable 'x', 'x' in f is bound to the nearest 'x' that was in scope when it was written.

A lambda is just a function, it does not necessarily imply there are free variables which it is closed over.

    function() { var y = 23; return y * 40; }

is a lambda with no free variables.

Technically the following implementation of evens is a closure:

    isEven x = (x `mod` 2) == 0
    
    evens xs = filter isEven xs

Can you see why? `isEven` is a free variable in evens which is bound to the isEven defined above it. evens is a closure, but generally we wouldn't refer to it as such.