Most browsers parse and discard a meaningless, trailing comma. Unfortunately, that's not the case for Internet Explorer, which in most versions throws a meaningless error. Therefore trailing commas should be eliminated.

Noncompliant Code Example

var settings = {
    'foo'  : oof,
    'bar' : rab,    // Noncompliant - trailing comma
};

Compliant Solution

var settings = {
    'foo'  : oof,
    'bar' : rab
};