How to replace last occurrence of characters in a string using javascript

Question

I'm having a problem finding out how to replace the last ', ' in a string with ' and ':

Having this string: test1, test2, test3

and I want to end out with: test1, test2 and test3

I'm trying something like this:

var dialog = 'test1, test2, test3';     dialog = dialog.replace(new RegExp(', /g').lastIndex, ' and '); 

but it's not working

Answer 1

foo.replace(/,([^,]*)$/, ' and $1') 

use the $ (end of line) anchor to give you your position, and look for a pattern to the right of the comma index which does not include any further commas.

Edit:

The above works exactly for the requirements defined (though the replacement string is arbitrarily loose) but based on criticism from comments the below better reflects the spirit of the original requirement.

console.log(      'test1, test2, test3'.replace(/,\s([^,]+)$/, ' and $1')   )