Why Doesn't Ko.observablearray.length Return Length Of Underlying Array?

Using Knockout, when working with an observableArray, you must grab the underlying array (myArray()) in order to read the length. I don't understand why myArray.length wouldn't ret

Solution 1:

This is because the plain items observable is in fact a Function, which has its own length property to indicate the number of arguments expected.

From MDN's page on Functions (properties section):

length Specifies the number of arguments expected by the function.

As a developer using the KnockoutJS library I'd also initially expect the length of an observableArray to be the length of the underlying array, but I do appreciate the KO library not overriding this Function property though, as that would probably cause other unwanted side-effects.

Solution 2:

This is because ko.observableArray is not really an array. It is a function that returns the underlying array.

In your example, since items is a function, you get a .length = 0.

Please check this fiddle where I have added spans with some additional properties

http://jsfiddle.net/LJVWE/3/