How to join the elements of an array such that the first letter is capital for all elements in JavaScript?

I want to join the elements of an array separated by commas and the first letter of each element to be capital, this should not affect the object values itself.

For example:

obj= ["apple","orange","lemon"]

Output should be:
Apple, Orange, Lemon.

Here is what I have tried and failed with:

obj.charAt(0).toUpperCase().join(', ')

>Solution :

Here is the code:

let a = ['apple', 'orange', 'lemon'];
let res = a.map(fruit => fruit.charAt(0).toUpperCase() + fruit.slice(1));
console.log(res); // [ "Apple", "Orange", "Lemon" ]