Ext JS: Elements in Combo are not visible, but loaded - ajax

Question

Ext JS 6.2.x is used. A combo is created. It uses ajax proxy request:
Request .../rest/maps/tree?_dc=1519213286176&page=1&start=0&limit=25
Request Method:GET
Status Code:200 OK
Accept:*/*
Accept-Encoding:gzip, deflate, br
Response headers:
Cache-Control:no-cache, no-store, must-revalidate
Connection:keep-alive
Content-Type:application/json
In response body a set of years is returned:
["2015","2017","2018","2019","2016","2020"]
Here is a code:
Ext.define('MapsYears', {
// extend: 'Ext.data.ArrayStore',
extend: 'Ext.data.Store',
alias: 'store.maps-years',
autoLoad: true,
fields: ['year'],
proxy: {
type: 'ajax',
url: 'rest/maps/tree'
}
});
Ext.define('Main.panel.SnapshotNow', {
xtype: 'snapshotNow',
extend: 'Ext.panel.Panel',
requires: [
],
items: [{
id: 'SnapshotNow',
xtype: "combobox",
store: {
type: 'maps-years'
},
displayField: 'year',
valueField: 'year'
}]
});
Items are loaded, I can even click on the combo, and the item appears as a chosen, but a list of items is not visible:
What do I miss?
UPDATE: In a response, it is not actually a json-format. I can fix this issue by changing rest service and returning a correct json. The question is, is there a way to tell ExtJS to process correctly list of elements in the original example, that looks like:
["2015","2017","2018","2019","2016","2020"]

Answer 1

This should fix your data structure
Ext.define('MapsYears', {
extend: 'Ext.data.Store',
alias: 'store.maps-years',
autoLoad: true,
fields: ['year'],
proxy: {
type: 'ajax',
url: 'rest/maps/tree',
reader: {
type: 'json',
transform: data => data.map(year => ({year}))
}
}
});