Question

I am using jQuery 1.7.1. and I have the following question/problem:

The code has as follows:

var accountObject = new Object();
accountObject.account = new Object();
accountObject.account.sas = [];

$.ajax({
    type: "PUT",
    url: "/a/2",
    data: accountObject,
    dataType: "html",
    success: function(msg) {
        alert_user("Successfully saved the selected session attributes as defaults");
    },
    error: function(msg) {
        alert_user(msg);            
    }
});

The problem is that, due to the fact that I set accountObject.account.sas to an empty array, the data arrives completely empty at the server, as:

{}

where it should have been:

{ "account": { "sas": [] } }

When I put some entries in the sas property of account then everything is ok. For example, if I put the string “1”, “2” and “3” as an array ["1", "2", "3"] then I get on the server:

{ "account": { "sas": [ "1", "2", "3" ] } }

Does anybody know why this is so?

Thanks in advance
Panayotis

Answer 1

The problem is that an empty array cannot be properly represented in a query string. When you pass the object hierarchy to data, jQuery will attempt to convert it to a query string, but can’t figure out what to do with an empty array.

The reason why 1.4.4 seemed to return an empty string whenever it got passed the same hierarchy was that it attempted to pass the key to the query string without a value, the result of which would be like: ...&property=&. This is by default interpreted as an empty string in most server environments.

I personally consider the behavior of 1.7.1 correct, because it forces the developer to check for parameter existence instead of mucking the type of the parameter.

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Some notes about various things mentioned here

• traditional: true is completely wrong, since it can never handle object hierarchies. What you get instead is: ...&key=[object Object], which is javascript’s toString() default result for all objects.

• JSON.stringify assigned to data will result in the entire thing passed as JSON to the query string, unless you combine it with processData: false, in which case you need to deserialize into meaningful objects “by hand” on the server side. It’s generally a useful option, but overkill in this case where a simple check would presumably have things working with minimal hassle.