remove the last comma and any whitespace after it with Javascript

This will remove the last comma and any whitespace after it:

str = str.replace(/,\s*$/, "");

It uses a regular expression:

• The / mark the beginning and end of the regular expression
• The , matches the comma
• The \s means whitespace characters (space, tab, etc) and the * means 0 or more
• The $ at the end signifies the end of the string