JavaScript异步回调有好处也有坏处，回调函数大量嵌套十分复杂．所以javascript中还有另一种异步处理模式叫promises．在AngularJS中的实现就是$q服务．
下面是一些小例子．
then,catch,finally
在链最后的 catch 为整个链式处理提供一个异常处理点
在链最后的 finally 总是会被执行，不管 promise 被处理或者被拒绝，起清理作用
<!DOCTYPE html> <html> <head> <meta content="width=device-width, initial-scale=1.0"> <link href="https://www.jb51.net/bootstrap.min.css" > <script src="https://www.jb51.net/jQuery.min.js"></script> <script src="https://www.jb51.net/angular.min.js"></script> <script src="https://www.jb51.net/bootstrap.min.js"></script> <script type="text/javascript"> var myapp = angular.module('myapp', []); myapp.controller('myController', function($scope, $q) { $scope.send = function() { var deferred = $q.defer(); var promise = deferred.promise; promise .then(function() { console.log('resolve.....') }, function() { console.log('reject.....'); }, function() { console.log('notify.....'); }) .catch(function() { console.log('catch..error..') }) .finally(function() { console.log('anywhere will be called..'); }); deferred.reject('resolve'); }; }); </script> <style type="text/css"> </style> </head> <body ng-app="myapp"> <div ng-controller="myController"> <button ng-click="send()">click</button> </div> </body> </html>
then第三个参数(表征状态)的应用
<!DOCTYPE html> <html> <head> <meta content="width=device-width, initial-scale=1.0"> <link href="https://www.jb51.net/bootstrap.min.css" > <script src="https://www.jb51.net/jquery.min.js"></script> <script src="https://www.jb51.net/angular.min.js"></script> <script src="https://www.jb51.net/bootstrap.min.js"></script> <script type="text/javascript"> var myapp = angular.module('myapp', []); myapp.controller('myController', function($scope, dataService) { $scope.send = function() { dataService.getData() .then(function success(data) { console.log(data); }, function error(error) { console.log(error); }, function status(process) { console.log(process); }); }; }); myapp.factory('dataService', function($q, $interval) { return { getData : function() { var deferred = $q.defer(); var process = 0; var interval = $interval(function() { process += 10; deferred.notify(process); //reject之后不再继续运行 // if (process == 50) { // deferred.reject(process); // } if (process >= 100) { $interval.cancel(interval); deferred.resolve(process); } }, 1000); return deferred.promise; } }; }); </script> <style type="text/css"> </style> </head> <body ng-app="myapp"> <div ng-controller="myController"> <button ng-click="send()">click</button> </div> </body> </html>
then链式
<!DOCTYPE html> <html> <head> <meta content="width=device-width, initial-scale=1.0"> <link href="https://www.jb51.net/bootstrap.min.css" > <script src="https://www.jb51.net/jquery.min.js"></script> <script src="https://www.jb51.net/angular.min.js"></script> <script src="https://www.jb51.net/bootstrap.min.js"></script> <script type="text/javascript"> var myapp = angular.module('myapp', []); myapp.controller('myController', function($scope, $q) { $scope.send = function() { var deferred = $q.defer(); var promise = deferred.promise; promise .then(function() { console.log('1.....') }) .then(function() { console.log('2....'); }); deferred.resolve('resolve'); }; }); </script> <style type="text/css"> </style> </head> <body ng-app="myapp"> <div ng-controller="myController"> <button ng-click="send()">click</button> </div> </body> </html>
then链会把上一个 then 的返回结果传递给调用链的下一个 then (如果没有就是 undefined).
<!DOCTYPE html> <html> <head> <meta content="width=device-width, initial-scale=1.0"> <link href="https://www.jb51.net/bootstrap.min.css" > <script src="https://www.jb51.net/jquery.min.js"></script> <script src="https://www.jb51.net/angular.min.js"></script> <script src="https://www.jb51.net/bootstrap.min.js"></script> <script type="text/javascript"> var myapp = angular.module('myapp', []); myapp.controller('myController', function($scope, $q, $timeout) { $scope.send = function() { var deferred = $q.defer(); var promise = deferred.promise; deferred.resolve('resolve'); promise .then(function(data) { console.log(data); var _deferred = $q.defer(); $timeout(function() { _deferred.resolve('resolve_'); }, 1000); return _deferred.promise; }) .then(function(data) { console.log(data); }); }; }); </script> <style type="text/css"> </style> </head> <body ng-app="myapp"> <div ng-controller="myController"> <button ng-click="send()">click</button> </div> </body> </html>
如果 then 返回一个 promise 对象，下一个 then 只会在这个 promise 被处理结束的时候调用。