js中的promise使用

 1 // 0.5秒后返回input*input的计算结果: 2 function multiply(input) { 3 ????return new Promise(function (resolve, reject) { 4 ????????log(‘calculating ‘ + input + ‘ x ‘ + input + ‘...‘); 5 ????????setTimeout(resolve, 500, input * input); 6 ????}); 7 } 8 ?9 // 0.5秒后返回input+input的计算结果:10 function add(input) {11 ????return new Promise(function (resolve, reject) {12 ????????log(‘calculating ‘ + input + ‘ + ‘ + input + ‘...‘);13 ????????setTimeout(resolve, 500, input + input);14 ????});15 }16 17 var p = new Promise(function (resolve, reject) {18 ????log(‘start new Promise...‘);19 ????resolve(123);20 });21 22 p.then(multiply)23 ?.then(add)24 ?.then(multiply)25 ?.then(add)26 ?.then(function (result) {27 ????log(‘Got value: ‘ + result);28 });

 1 ‘use strict‘; 2 ?3 // ajax函数将返回Promise对象: 4 function ajax(method, url, data) { 5 ????var request = new XMLHttpRequest(); 6 ????return new Promise(function (resolve, reject) { 7 ????????request.onreadystatechange = function () { 8 ????????????if (request.readyState === 4) { 9 ????????????????if (request.status === 200) {10 ????????????????????resolve(request.responseText);11 ????????????????} else {12 ????????????????????reject(request.status);13 ????????????????}14 ????????????}15 ????????};16 ????????request.open(method, url);17 ????????request.send(data);18 ????});19 }20 21 var log = document.getElementById(‘test-promise-ajax-result‘);22 var p = ajax(‘GET‘, ‘/api/categories‘);23 p.then(function (text) { // 如果AJAX成功，获得响应内容24 ????25 ????console.log(text);26 },function (status) { // 如果AJAX失败，获得响应代码27 ????console.log(‘ERROR: ‘ + status);28 });