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diff --git a/files/zh-tw/web/javascript/reference/global_objects/promise/catch/index.html b/files/zh-tw/web/javascript/reference/global_objects/promise/catch/index.html new file mode 100644 index 0000000000..d06036c11e --- /dev/null +++ b/files/zh-tw/web/javascript/reference/global_objects/promise/catch/index.html @@ -0,0 +1,189 @@ +--- +title: Promise.prototype.catch() +slug: Web/JavaScript/Reference/Global_Objects/Promise/catch +tags: + - EMCAScript 2015 + - JavaScript + - Method + - Promise + - Prototype +translation_of: Web/JavaScript/Reference/Global_Objects/Promise/catch +--- +<div>{{JSRef}}</div> + +<p><strong>catch()</strong> 方法只處理 Promise 的被拒絕狀態，並回傳一個新的 <code>Promise</code> 物件。此方法的行為等同於呼叫 {{jsxref("Promise.then", "Promise.prototype.then(undefined, onRejected)")}}。</p> + +<h2 id="語法">語法</h2> + +<pre class="syntaxbox"><var>p.catch(onRejected)</var>; + +p.catch(function(reason) { + // rejection +}); +</pre> + +<h3 id="參數">參數</h3> + +<dl> + <dt>onRejected</dt> + <dd>一個 {{jsxref("Function")}} ，在 <code>Promise</code> 被拒絕時被呼叫。這個函式有一個引數： + <dl> + <dt><code>reason</code></dt> + <dd>失敗訊息。</dd> + </dl> + 若 onRejected 拋出一個錯誤或回傳一個被拒絕的 Promise，則 catch() 回傳的 Promise 被拒絕；其他情形都是被實現。</dd> +</dl> + +<h3 id="回傳值">回傳值</h3> + +<p>呼叫（<code>catch</code> 的 promise）物件，內部呼叫 <code>Promise.prototype.then</code>，傳入引數 undefined 及 onRejected；接著以之結果回傳（結果為 {{jsxref("Promise")}}）。</p> + +<p><strong>內部呼叫演示：</strong></p> + +<pre class="brush: js">// overriding original Promise.prototype.then/catch just to add some logs +(function(Promise){ + var originalThen = Promise.prototype.then; + var originalCatch = Promise.prototype.catch; + + Promise.prototype.then = function(){ + console.log('> > > > > > called .then on %o with arguments: %o', this, arguments); + return originalThen.apply(this, arguments); + }; + Promise.prototype.catch = function(){ + console.log('> > > > > > called .catch on %o with arguments: %o', this, arguments); + return originalCatch.apply(this, arguments); + }; + +})(this.Promise); + + + +// calling catch on an already resolved promise +Promise.resolve().catch(function XXX(){}); + +// logs: +// > > > > > > called .catch on Promise{} with arguments: Arguments{1} [0: function XXX()] +// > > > > > > called .then on Promise{} with arguments: Arguments{2} [0: undefined, 1: function XXX()] +</pre> + +<h2 id="描述">描述</h2> + +<p><code>catch</code> 方法在處理 promise 組合的錯誤時很有幫助。</p> + +<h2 id="範例">範例</h2> + +<h3 id="使用及串接_catch_方法">使用及串接 <code>catch</code> 方法</h3> + +<pre class="brush: js">var p1 = new Promise(function(resolve, reject) { + resolve('Success'); +}); + +p1.then(function(value) { + console.log(value); // "Success!" + throw 'oh, no!'; +}).catch(function(e) { + console.log(e); // "oh, no!" +}).then(function(){ + console.log('after a catch the chain is restored'); +}, function () { + console.log('Not fired due to the catch'); +}); + +// The following behaves the same as above +p1.then(function(value) { + console.log(value); // "Success!" + return Promise.reject('oh, no!'); +}).catch(function(e) { + console.log(e); // "oh, no!" +}).then(function(){ + console.log('after a catch the chain is restored'); +}, function () { + console.log('Not fired due to the catch'); +}); +</pre> + +<h3 id="拋出例外時的陷阱">拋出例外時的陷阱</h3> + +<pre class="brush: js">// Throwing an error will call the catch method most of the time +var p1 = new Promise(function(resolve, reject) { + throw 'Uh-oh!'; +}); + +p1.catch(function(e) { + console.log(e); // "Uh-oh!" +}); + +// Errors thrown inside asynchronous functions will act like uncaught errors +var p2 = new Promise(function(resolve, reject) { + setTimeout(function() { + throw 'Uncaught Exception!'; + }, 1000); +}); + +p2.catch(function(e) { + console.log(e); // This is never called +}); + +// Errors thrown after resolve is called will be silenced +var p3 = new Promise(function(resolve, reject) { + resolve(); + throw 'Silenced Exception!'; +}); + +p3.catch(function(e) { + console.log(e); // This is never called +});</pre> + +<h3 id="如果_Promise_被實現">如果 Promise 被實現</h3> + +<pre class="brush: js">//Create a promise which would not call onReject +var p1 = Promise.resolve("calling next"); + +var p2 = p1.catch(function (reason) { + //This is never called + console.log("catch p1!"); + console.log(reason); +}); + +p2.then(function (value) { + console.log("next promise's onFulfilled"); /* next promise's onFulfilled */ + console.log(value); /* calling next */ +}, function (reason) { + console.log("next promise's onRejected"); + console.log(reason); +});</pre> + +<h2 id="規範">規範</h2> + +<table class="standard-table"> + <tbody> + <tr> + <th scope="col">Specification</th> + <th scope="col">Status</th> + <th scope="col">Comment</th> + </tr> + <tr> + <td>{{SpecName('ES2015', '#sec-promise.prototype.catch', 'Promise.prototype.catch')}}</td> + <td>{{Spec2('ES2015')}}</td> + <td>Initial definition in an ECMA standard.</td> + </tr> + <tr> + <td>{{SpecName('ESDraft', '#sec-promise.prototype.catch', 'Promise.prototype.catch')}}</td> + <td>{{Spec2('ESDraft')}}</td> + <td> </td> + </tr> + </tbody> +</table> + +<h2 id="瀏覽器相容性">瀏覽器相容性</h2> + +<p class="hidden">To contribute to this compatibility data, please write a pull request against this repository: <a href="https://github.com/mdn/browser-compat-data">https://github.com/mdn/browser-compat-data</a>.</p> + +<p>{{Compat("javascript.builtins.Promise.catch")}}</p> + +<h2 id="參見">參見</h2> + +<ul> + <li>{{jsxref("Promise")}}</li> + <li>{{jsxref("Promise.prototype.then()")}}</li> +</ul> |