There's a method to iterate over only own object properties, not including prototype's ones:

for (var i in array) if (array.hasOwnProperty(i)) {
    // do something with array[i]
}

but it still will iterate over custom-defined properties.

In javascript any custom property could be assigned to any object including array.

If one wants to iterate over sparsed array, for (var i = 0; i < array.length; i++) if (i in array) or array.forEach with es5shim should be used.

There's a method to iterate over only own object properties, not including prototype's ones:

for (var i in array) if (array.hasOwnProperty(i)) {
    // Do something with array[i]
}

but it still will iterate over custom-defined properties.

In JavaScript any custom property could be assigned to any object, including an array.

If one wants to iterate over sparsed array, for (var i = 0; i < array.length; i++) if (i in array) or array.forEach with es5shim should be used.