javascript - 数组和对象中的尾部逗号是否属于规范的一部分？(Are trailing commas in arrays and objects part of the spec?)

Question

Are trailing commas standard in JavaScript, or do most browsers like Chrome and Firefox just tolerate them?(JavaScript中的尾部逗号是标准格式，还是像Chrome和Firefox这样的大多数浏览器都可以接受？)

I thought they were standard, but IE8 puked after encountering one—of course IE not supporting something hardly means it's not standard.(我以为它们是标准的，但是IE8在遇到一个标准后就呕吐了—当然IE 8不支持某些功能也不意味着它不是标准的。)

Here's an example of what I mean (after the last element of the books array):(这是我的意思的示例（在books数组的最后一个元素之后）：)

var viewModel = {
    books: ko.observableArray([
        { title: "..", display: function() { return ".."; } },
        { title: "..", display: function() { return ".."; } },
        { title: "..", display: function() { return ".."; } }, // <--right there
    ]),
    currentTemplate: ko.observable("bookTemplate1"),
    displayTemplate: function() { return viewModel.currentTemplate(); }
};

  ask by Adam Rackis translate from so

Answer 1

Specs: ECMAScript 5 and ECMAScript 3(规格： ECMAScript 5和ECMAScript 3)

---

Section 11.1.5 in the ECMAScript 5 specification:(ECMAScript 5规范中的11.1.5节 ：)

ObjectLiteral :
    { }
    { PropertyNameAndValueList }
    { PropertyNameAndValueList , }

So yes, it is part of the specification.(是的，它是规范的一部分。)

Update: Apparently this is new in ES5.(更新：显然，这是ES5中的新功能。)

In ES3 (page 41), the definition was just:(在ES3（第41页）中，定义仅为：)

ObjectLiteral :
    { }
    { PropertyNameAndValueList }

---

For arrays literals ( Section 11.1.4 ) it is even more interesting ( Update: this already existed in ES3):(对于数组文字（ 第11.1.4节 ），它甚至更有趣（ 更新： ES3中已经存在）：)

ArrayLiteral :
    [ Elisionopt ]
    [ ElementList ]
    [ ElementList , Elision_opt ]

(where Elision_opt is Elision _opt , meaning the Elision is optional)(（其中Elision_opt是Elision _opt ，这意味着Elision是可选的）)

Elision is defined as(Elision定义为)

Elision :
    ,
    Elision ,

So, an array literal like(因此，像这样的数组文字)

var arr = [1,2,,,,];

is perfectly legal.(是完全合法的。)

This creates an array with two elements but sets the array length to 2 + 3 = 5 .(这将创建一个包含两个元素的数组，但是将数组长度设置为2 + 3 = 5 。)

Don't expect too much from IE (before IE9)...(不要对IE期望太多（在IE9之前）...)