How Can I Get A Value Field From A Store

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ExtJS

I created a store with ExtJS 3.4 , here is my code :

 var itiStore = new Ext.data.JsonStore({
    root: 'getItiResultResult',
    fields: [
        {name: 'Arrival'},
        {name: 'ColumnsName'},
        {name: 'Error'},
        {name: 'Points', mapping: 'Points'},
        {name: 'La', mapping: 'Points.La'},
        {name: 'Lo', mapping: 'Points.Lo'},
        {name: 'Rows', mapping: 'Rows'},
        {name: "ChangeRowColor", mapping: 'Rows.ChangeRowColor'},
        {name: "CumDistance", mapping: 'Rows.CumDistance'},
        {name: "CumTime", mapping: 'Rows.CumTime'},
        {name: "Direction", mapping: 'Rows.Direction'},
        {name: "Distance", mapping: 'Rows.Distance'},
        {name: "La", mapping: 'Rows.La'},
        {name: "Lo", mapping: 'Rows.Lo'},
        {name: "RoadMap", mapping: 'Rows.RoadMap'},
        {name: "Step", mapping: 'Rows.Step'},
        {name: "Time", mapping: 'Rows.Time'},
        {name: "dCumDist", mapping: 'Rows.dCumDist'},
        {name: "dCumTime", mapping: 'Rows.dCumTime'},
        {name: 'Start'},
        {name: 'TotDistance'},
        {name: 'TotTime'}
    ]
});
>

I used to show my store :

itiStore.loadData(Ext.decode(response.responseText), false); console.log(JSON.parse(response.responseText)); 
>

how can i get just the value of the field 'RoadMap' and recuperate it to show it apart ?

Thank you guys in advance for your help.