Try this it works fine for me.
Ext.onReady(function() {
Ext.define('Ext.form.field.Month', {
extend: 'Ext.form.field.Date',
alias: 'widget.monthfield',
requires: ['Ext.picker.Month'],
alternateClassName: ['Ext.form.MonthField', 'Ext.form.Month'],
selectMonth: null,
createPicker: function() {
var me = this,
format = Ext.String.format;
return Ext.create('Ext.picker.Month', {
pickerField: me,
ownerCt: me.ownerCt,
renderTo: document.body,
floating: true,
hidden: true,
focusOnShow: true,
minDate: me.minValue,
maxDate: me.maxValue,
disabledDatesRE: me.disabledDatesRE,
disabledDatesText: me.disabledDatesText,
disabledDays: me.disabledDays,
disabledDaysText: me.disabledDaysText,
format: me.format,
showToday: me.showToday,
startDay: me.startDay,
minText: format(me.minText, me.formatDate(me.minValue)),
maxText: format(me.maxText, me.formatDate(me.maxValue)),
listeners: {
select: {
scope: me,
fn: me.onSelect
},
monthdblclick: {
scope: me,
fn: me.onOKClick
},
yeardblclick: {
scope: me,
fn: me.onOKClick
},
OkClick: {
scope: me,
fn: me.onOKClick
},
CancelClick: {
scope: me,
fn: me.onCancelClick
}
},
keyNavConfig: {
esc: function() {
me.collapse();
}
}
});
},
onCancelClick: function() {
var me = this;
me.selectMonth = null;
me.collapse();
},
onOKClick: function() {
var me = this;
if (me.selectMonth) {
me.setValue(me.selectMonth);
me.fireEvent('select', me, me.selectMonth);
}
me.collapse();
},
onSelect: function(m, d) {
var me = this;
me.selectMonth = new Date((d[0] + 1) + '/1/' + d[1]);
}
});
Ext.create('Ext.form.field.Month', {
format: 'F, Y',
fieldLabel: 'Date',
renderTo: Ext.getBody()
});
});