Modern browsers ignore unneeded, trailing commas, so there are no negatives to having them unless you’re supporting an IE 8 application. Since they make adding new properties simpler, their use is preferred. This rule raises an issue when the last item in a multiline construct (array or object literal, import or export statement, function declaration or call) does not end with a trailing comma and does not lie on the same line as the closing curly brace, bracket or parenthesis.

Noncompliant Code Example

var joe = {
  fname: "Joe",
  lname: "Smith"      // Noncompliant
};

Compliant Solution

var joe = {
  fname: "Joe",
  lname: "Smith",    // OK
};

var joe = {
  fname: "Joe",
  lname: "Smith"};   // OK