Your array is fine your just seeing the output as a string, try just logging the array by itself
console.log(arrayz);
also might I suggest some simplification of your jstl.
var arrayz = [
<c:forEach var="item" items="${list}" varStatus="s">
["'" + "${item.date}".substring(0,7) + "'", ${item.price}]${!s.last?',':''}
</c:forEach>
]