Ext.data.SingleRecordJsonReader demonstrates how to modify the Ext JS JsonReader (see http://thorben.ziemek.de/blog/2011/07/singlerecordjsonreader/)

classic.json

{
    root: [{
        field1:value1,
        field2:value1
    },{
        field1:value2,
        field2:value2
    }]
}

singleRecord.json

{
    root: {
        field1:value1,
        field2:value1
    }
}

SingleRecordJsonReader.js

Ext.ns('Ext.data');
 
Ext.data.SingleRecordJsonReader = Ext.extend(Ext.data.JsonReader, {
 
    readRecords: function(data) {
        var root = this.root;
        data[root] = [data[root]];
        return Ext.data.SingleRecordJsonReader.superclass.readRecords.call(this, data);
    }
 
});
 
Ext.data.ReaderMgr.registerType('singlejson', Ext.data.SingleRecordJsonReader);