如何防止多个“，”被附加在字符串中

Question

I am trying to basically check if the string ends with ", " then do not append another ", " . If the string does not end with ", " then append ", ". I just want one ", " in between two strings. However as I hit the "compute" button of my script several times (which basically iterates the key values & appends the comma's between strings) , I get multiple ", " between two strings. What I tried does not really work.

eg:

Expected is abc, apple, pear, strawberry even if I hit compute many times or one time

What I get after multiple clicks of compute button:

abc, , , , apple, , , , pear, , , , strawberry

Here's what I tried:

//Here obj[key][i] is the string

var lenson = obj[key][i].length;
if(1!=len-1){
if(obj[key][i].charAt(lenson-1) === " " && obj[key][i].charAt(lenson-2)=== ","){

}
else{
if(obj[key][i]!=""){
obj[key][i]+=", ";
}
}
li.appendChild(document.createTextNode( obj[key][i] ));

}

Answer 1

I am assuming you are getting your data from some sort of json object or similar. Since you are already looping over the keys, my advice would be to simple store them in an array. Then when you want to output them to string you just use .join(",")

var list = yourarray.join(",");