Set the initial value of a Select from fetched data
<Component name="Test" var.selectedValue="">
<DataSource
id="myData"
url="/api/users_initial_value"
onLoaded="(data) => { selectedValue = data[0].id }"
/>
<Select initialValue="{selectedValue}">
<Items data="{myData}">
<Option value="{$item.id}" label="{$item.username}" />
</Items>
</Select>
</Component>
<Component name="Test" var.selectedValue="">
<DataSource
id="myData"
url="/api/users_initial_value"
onLoaded="(data) => { selectedValue = data[0].id }"
/>
<Select initialValue="{selectedValue}">
<Items data="{myData}">
<Option value="{$item.id}" label="{$item.username}" />
</Items>
</Select>
</Component>