I am absolutely new to Mathematica Online. Using Mathematica 10.1.0.0 on my MacBook Pro (OS X 10.10.3), the following code works perfectly.
Manipulate[
Graphics[{
Blue,
Arrow[{{0, 0}, arrowA}],
Arrow[{{0, 0}, arrowB}]
},
PlotRange -> 5,
Axes -> True, AxesLabel -> {"x", "y"},
PlotLabel ->
Row[{"\[Theta] = ",
NumberForm[angleBetweenVectors[arrowA, arrowB], {3, 1}],
"\[Degree]"}]
],
{{arrowA, {3, 3}}, Locator},
{{arrowB, {-3, 3}}, Locator},
Initialization :> (
angleBetweenVectors[u_, v_] :=
ArcCos[(u.v)/(Norm[u] Norm[v])]/Degree // N
)
]
However, when I enter it on Mathematica Online, I get the following result.

Does this mean that Manipulate is limited when used on Mathematica Online? If so, is there documentation that says what will work and what will not?
Dynamicsdid not work. Here is a link that lists something that did not work then Cloud Dynamic support – Nasser May 30 '15 at 05:30