如何使用AJAX在Javascript中通过PHP数组索引?

I am very new to PHP and Javascript. I would like to use a PHP function in order to fetch database data as an array and be able to use it in Javascript. I am I have searched online but I haven't come across anything that helps my particular situation. How would I get the array in Javascript and be able to use it like so: I am very new to PHP and Javascript. I would li