Why does for(var i in Math) not iterate through Math.* in Javascript?

Question

For some reason for(var i in Math){console.log(i)} doesn\'t show the expected tan, cos, atan2, E, PI in Javascript.

Answer 1

Those properties are non-enumerable.

From the MDC documentation on for..in:

A for...in loop does not iterate over built-in properties.

In newer JavaScript implementations you can make your own non-enumerable properties. Check out propertyIsEnumerable() and Object.defineProperty().