Firstly, sorry for my not very good english!
I need make next thing: ExtJS 3.4 Editable Grid (example), which will work with json format. Input source is in json format. I did it, all work fine, like in example.
I did:
- data downloading from database to array in php
- array is encoded to json format
- editable grid source is a page with json message now all working fine.
Now I need make this: I need to update data in database on cell updating in grid.
How can I do this? Didn't find anything in web. 
Maybe there are some method like 'OnCellEditting' like in delphi7?
My js code:
Ext.onReady(function () {
    function formatDate(value) {
        return value ? value.dateFormat('M d, Y') : '';
    }
    // shorthand alias
    var fm = Ext.form;
    // the column model has information about grid columns
    // dataIndex maps the column to the specific data field in
    // the data store (created below)
    var cm = new Ext.grid.ColumnModel({
        // specify any defaults for each column
        defaults: {
            sortable: false // columns are not sortable by default           
        },
        columns: [{
            header: 'ID',
            dataIndex: 'id',
            width: 30
        }, {
            id: 'firstname',
            header: 'Firstname',
            dataIndex: 'firstname',
            width: 220,
            // use shorthand alias defined above
            editor: new fm.TextField({
                allowBlank: false
            })
        }, {
            header: 'Lastname',
            dataIndex: 'lastname',
            width: 220,
            // use shorthand alias defined above
            editor: new fm.TextField({
                allowBlank: false
            })
        }]
    });
    // create the Data Store
    var store = new Ext.data.JsonStore({
        totalProperty: 'total', // total data, see json output
        root: 'results', // see json output
        url: '/grid/json',
        fields: [
            'firstname', 'lastname']
    });
    // create the editor grid
    var grid = new Ext.grid.EditorGridPanel({
        store: store,
        cm: cm,
        renderTo: 'grid-editable',
        width: 440,
        height: 300,
        autoExpandColumn: 'firstname', // column with this id will be expanded
        title: 'Edit Plants?',
        frame: true,
        clicksToEdit: 1
    });
    // manually trigger the data store load
    store.load({
        // store loading is asynchronous, use a load listener or callback to handle results
    });
});
 
                        
The easiest way for you is to send an ajax request on each change
but I think you should take a look at the extjs examples and read more about the Store communication with the server (for example with REST).