Access JSON or JS property using string

I have a JSON array like this:

_htaItems = [
    {"ID":1,
     "parentColumnSortID":"0",
     "description":"Precondition",
     "columnSortID":"1",
     "itemType":0},
    {"ID":2,
     "parentColumnSortID":"0",
     "description":"Precondition",
     "columnSortID":"1",
    "itemType":0}]

I want to update this by passing the ID, column name and new value to a function:

    function updateJSON(ID, columnName, newValue)
    {
        var i = 0;
        for (i = 0; i < _htaItems.length; i++)
        {
            if (_htaItems[i].ID == ID)
            {
                ?????
            }
        }
    }  

My question is, how do I update the value? I know I can do something like the following:

 _htaItems[x].description = 'New Value'

But in my cause, the column name is being passed as a string.