Question

I wonder why putting a comma at the end of a single element is legal in a JavaScript array:

var array = [
    'foo', // no error in IDE
]

while putting it at the end of a single element in an object is illegal (at least my IDE – WebStorm – is flagging about an error):

var object = {
    'foo': 'bar', // error in IDE
}

Is this really illegal in JavaScript?

Answer 1

In the ECMAScript 5 specification it is legal:

ObjectLiteral : 
    { } 
    { PropertyNameAndValueList } 
    { PropertyNameAndValueList , } 

It was illegal in ECMAScript 3.

ObjectLiteral : 
    { } 
    { PropertyNameAndValueList } 

I believe it was made legal to make things like this doable.

function getItems() {
    return {
        one : 1,
        two : 2,
        three : 3,
        //four : 4,
    };
}

Instead of this:

function getItems() {
    return {
        one : 1,
        two : 2,
        three : 3//,
        //four : 4,
    };
}

Saving some of the programmers time.