我有一个Angular ui-boostrap typeahead组件正常工作，直到我向整个函数添加了一个要求。我想在用户输入3个字母后立即调用后端的建议结果。这是正确完成但我的问题是只有当用户键入第4个字母时结果才可见。有没有办法绕过这个，通过强制它在用户输入第三个字母后刷新UI。 代码是：
HTLM
<input name="states" id="states" type="text" ng-model="vm.cityName"
uib-typeahead="municipality as municipality.city + ' (' + municipality.name + ') '+municipality.zipCode for municipality in vm.getMunicipalitiesByCity($viewValue) | filter:$viewValue | limitTo:8" class="form-control" typeahead-on-select="vm.citySelected()" >
JS Controller
vm.getMunicipalitiesByCity = function (cityName) {
if (cityName != undefined && cityName.length == 3) {
CalculationEndpointService.municipalitiesByCity({cityName: cityName}, function (result) {
vm.municipalities = result.map(
function (item) {
return item;
}
);
});
}
if(cityName.length<3){
vm.municipalities=[""];
}
return vm.municipalities;
};