Start by defining your arry like this example here:
var items = [12, 548 , 'a' , 2 , 5478 , 'foo' , 8852, , 'Doe' , 2145 , 119];
Then use Math.random() like in the code below. Important to remember here is that Math.random() gives a float which is a number that may contain decimals so you need to use Math.floor() to make sure the final number is an integer that can be used as an array index.
var randomItem = items[Math.floor(Math.random() * items.length)];
And that's it, randomItem now holds the value of your random array item.