APEX version: 5.1 on apex.oracle.com
This is valid javascript as tested here
var LOV =new Array();
LOV = ['cuis', 'carpincho'];
alert('length =' + LOV.length);
it produces the expected output:

But if I put that javascript code in APEX 5, on a Dynamic action, I get this error: "Uncaught SyntaxError: Unexpected token var"

Is there a special way in which arrays should be declared here?