This way is easiest one in my opinion.
var nameList = new Array('item1','item2','item3','item4');
// Using for loop to loop through each item to check if item exist.
for (var i = 0; i < nameList.length; i++) {
if (nameList[i] === 'item1')
{
alert('Value exist');
}else{
alert('Value doesn\'t exist');
}
And Maybe Another way to do it is.
nameList.forEach(function(ItemList)
{
if(ItemList.name == 'item1')
{
alert('Item Exist');
}
}