Array Declaration On FF Vs IE

There is something that I don't understand well, I use array for
combining strings like

items = ['hello world', ', how are you', '?', 'the end'].join('');

in FF this works well but in IE I had to add something like this

var items = new Array();
items = ['hello world', ', how are you', '?', 'the end'].join('');

My question is why is there a need for var items = new Array(): and
why items = new Array(); doesn't work? I don't want the items to be a
global variable, since it was declare inside a function I want it to
be local only.