javascript - 多次调用[promise的]解析

Question

这个问题已经有答案了:

What happens when a promise is resolved multiple times (2 个回答)

已关闭 5 年前。

我有这个函数，它在异步获取数据时返回一个 promise 。正如您所看到的，该 Promise 的代码 ($watchCollection) 中有一些观察者，它们会持续观察数据并为每次更改触发 Promise 的解析函数。

我无法测试 then 是否会为每个解析函数调用触发多次。这可能吗？

this.getGridDataAndMetaData = function(viewId) {          

    return new Promise(function(resolve, reject) {

        dataStore.fetchView(viewId)
            .then(function(viewEntity) {

                var grid_groupement = viewEntity.descriptor.state ? viewEntity.descriptor.state.grid_groupement : undefined;
                var dataStoreEntities = viewEntity.getEntityType().getEntities();
                var dataStoreProperties = viewEntity.getEntityType().getProperties();

                var gridDataAndMetaData;

                $rootScope.$watchCollection(function() {
                        return dataStoreEntities;
                    },
                    function(newCollection, oldCollection) {    

                        if (!angular.equals(newCollection, {}))
                            formatDataStoreEntities(angular.copy(newCollection), grid_groupement)
                            .then(function(data) {  


                                gridDataAndMetaData = data;                                            

                                if (lastNewProperties != undefined && !angular.equals(lastNewProperties, [])) {
                                    data.viewEntity = viewEntity;
                                    data.grid_groupement = grid_groupement;
                                    data.properties = lastNewProperties;   

                                    resolve(data);
                                }
                            });

                    });

                $rootScope.$watchCollection(function() {
                        return dataStoreProperties;
                    },
                    function(newProperties, oldProperties) {                                    
                        lastNewProperties = angular.copy(newProperties);                                    
                        if (gridDataAndMetaData != undefined && !angular.equals(gridDataAndMetaData.valuesIdsEntitiesTabFormat, {})) {                                                        
                            generateServiceTabs(newProperties, function() {
                                data.viewEntity = viewEntity;
                                data.grid_groupement = grid_groupement;
                                data.properties = lastNewProperties;

                                resolve(data);
                            });
                        }
                    });
            }).catch(function(error) {
                console.error('%c getGridDataAndMetaData :: dataStore.fetchView(viewId):: error : ' + JSON.stringify(error), 'background: red; color: white; display: block;');
                reject(error);
            });


    });

}

Answer 1

resolve 函数是 Promise 执行器函数的参数，最多执行一次。 Promise 只能实现一次。请注意，给定的 dataStore.fetchView(viewId) 返回一个 Promise，Promise 构造函数不是必需的。