Promise 代表异步操作的最终结果。jQuery 用它自己的方式处理 promises，原生 JavaScript 遵循 Promises/A+ 标准实现了最小 API 来处理 promises。

• 7.1 done, fail, always done 会在 promise 解决时调用，fail 会在 promise 拒绝时调用，always 总会调用。 // jQuery$promise.done(doneCallback).fail(failCallback).always(alwaysCallback)// Nativepromise.then(doneCallback, failCallback).then(alwaysCallback, alwaysCallback)
• 7.2 when when 用于处理多个 promises。当全部 promises 被解决时返回，当任一 promise 被拒绝时拒绝。 // jQuery$.when($promise1, $promise2).done((promise1Result, promise2Result) => {});// NativePromise.all([$promise1, $promise2]).then([promise1Result, promise2Result] => {});
• 7.3 Deferred Deferred 是创建 promises 的一种方式。 // jQueryfunction asyncFunc() { const defer = new $.Deferred(); setTimeout(() => { if(true) { defer.resolve(‘some_value_computed_asynchronously’); } else { defer.reject(‘failed’); } }, 1000); return defer.promise();}// Nativefunction asyncFunc() { return new Promise((resolve, reject) => { setTimeout(() => { if (true) { resolve(‘some_value_computed_asynchronously’); } else { reject(‘failed’); } }, 1000); });}// Deferred wayfunction defer() { const deferred = {}; const promise = new Promise((resolve, reject) => { deferred.resolve = resolve; deferred.reject = reject; }); deferred.promise = () => { return promise; }; return deferred;}function asyncFunc() { const defer = defer(); setTimeout(() => { if(true) { defer.resolve(‘some_value_computed_asynchronously’); } else { defer.reject(‘failed’); } }, 1000); return defer.promise();}