Question

If I create a JavaScript object like:

var lst = [];
var row = [];
row.Col1 = 'val1';
row.Col2 = 'val2'; 
lst.push(row);

And then convert it to a string:

JSON.stringify(lst);

The result is an object containing an empty object:

[[]]

I would expect it to serialize like:

[[Col1 : 'val1', Col2: 'val2']]

Why do the inner objects properties not serialize?

Code snippet at JSFiddle.

Answer 1

Because row is an array, not an object. Change it to:

var row = {};  

This creates an object literal. Your code will then result in an array of objects (containing a single object):

[{"Col1":"val1","Col2":"val2"}]

Update

To see what really happens, you can look at json2.js on GitHub. This is a (heavily reduced) snippet from the str function (called by JSON.stringify):

if (Object.prototype.toString.apply(value) === '[object Array]') {
    //...
    length = value.length;
    for (i = 0; i < length; i += 1) {
        partial[i] = str(i, value) || 'null';
    }
    //...
}
//...
for (k in value) {
    if (Object.prototype.hasOwnProperty.call(value, k)) {
        //...
    }
    //...
}
//...

Notice that arrays are iterated over with a normal for loop, which only enumerates the array elements. Objects are iterated with a for...in loop, with a hasOwnProperty test to make sure the proeprty actually belongs to this object.