merge two arrays with a separator, javascript

I am trying to merge two arrays and have a separator included between all values (comma). I tried this:

var aAndBWithCommasInBetween = a.concat(b);

But that leads to:

DealerOrigin

instead of:

Dealer, Origin

each a and b can have many values or none.

Answer

your a and b in the example are not arrays but strings, which is why concat creates another string.

['Apple'].concat(['Orange'])
["Apple", "Orange"]

versus

"Apple".concat("Orange")
"AppleOrange"

You could be looking for array.join(), which converts an array into a single string separated by commas or whatever separator you pass in.

["Apple", "Orange"].join(',')
"Apple,Orange"