Are trailing commas or missing keys acceptable in JavaScript object notation?

I have created a code generator and I am contemplating whether or not to address the issue of the extra comma at the end. While Internet Explorer seems to ignore it, I want to ensure cross-browser compatibility and generate valid code.

function init() {
var myOptions = { : 'Select home value', // <== THERE'S THE NON EXISTANT KEY
100000 : '$90,001 - $100,000',
1000000 : '$950,001 - $1,000,000',
1000001 : 'Over $1,000,000', // <== HERE'S THE COMMA I'M CURIOUS ABOUT
};

Here is the code that is being generated

protected string DoTransform()
{
    var sb = new StringBuilder("var myOptions = {");
    foreach (var option in 
        XDocument.Load(MapPath("~/App_Data/Data.xml"))
            .XPathSelectElements("./data/options[@question='ApproximatePropertyValue']/option"))
    {
        sb.AppendFormat("{0} : '{1}',\n", option.Attribute("value").Value, option.Value);
    }
    sb.AppendLine("};");
    return sb.ToString();
}

ANSWER: Here is the updated code that handles the empty key (by skipping the first element) and trailing comma (by reorganizing logic for TrimEnd to remove it).

protected string DoTransform()
{
    var sb = new StringBuilder();
    foreach (var option in 
        XDocument.Load(MapPath("~/App_Data/Data.xml"))
            .XPathSelectElements("./data/options[@question='ApproximatePropertyValue']/option")
            .Skip(1))
    {
        sb.AppendFormat("{0}:'{1}',", option.Attribute("value").Value, option.Value);
    }
    return"var myOptions = {\n" + sb.ToString().TrimEnd(',') + "};";
}

Answer №1

It has come to my attention that while most browsers may tolerate a trailing comma, it is not compliant with the JSON specification, making it a risky move. However, omitting a key in the initial key-value pair will not go unnoticed by anyone ;-)

Edit

I have just reviewed your code snippet. Apologies, my familiarity with .NET is limited (practically nonexistent), but I believe the following solution should work:

foreach (var option in 
    XDocument.Load(MapPath("~/App_Data/Data.xml"))
       .XPathSelectElements(
             "./data/options[@question='ApproximatePropertyValue']/option"
       )
    )
{
    // The length serves as an indicator; if added to, it surpasses 16
    if(sb.Length > 20)sb.Append(",");
    sb.AppendFormat("\n{0} : '{1}'", 
        option.Attribute("value").Value, option.Value);
}

Answer №2

According to Opera 12:

[14.07.2011 03:44:53] JavaScript - ...
Inline script compilation
Syntax error at line 6 while loading:
  var myOptions = {: 'Select home value
-------------------^
expected '}', got ':'

Suggesting to consider using a library from http://json.org/ instead of reinventing the wheel.

(Shh, keep this between us:) One possible workaround could be appending a sentinel like "_ignore_me": false to the sb.

Answer №3

Trailing commas can cause issues in Internet Explorer 7 and earlier versions. However, the behavior may vary based on the document mode in newer versions.

Answer №4

Internet Explorer doesn't play nice with those pesky trailing commas, but don't worry - other browsers have got your back!

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