path: root/files/tr/web/javascript/reference/global_objects/promise/catch/index.html

---
title: Promise.prototype.catch()
slug: Web/JavaScript/Reference/Global_Objects/Promise/catch
tags:
  - JavaScript
  - Promise
  - Prototype
  - fonksiyon
  - metod
translation_of: Web/JavaScript/Reference/Global_Objects/Promise/catch
---
<div>{{JSRef}}</div>

<p>The <strong>catch()</strong> method returns a <code>Promise</code> and deals with rejected cases only. It behaves the same as calling {{jsxref("Promise.then", "Promise.prototype.then(undefined, onRejected)")}} (in fact, calling <code>obj.catch(onRejected)</code> internally calls <code>obj.then(undefined, onRejected)</code>). This means, that you have to provide <code>onRejected</code> function even if you want to fallback to <code>undefined</code> result value - for example <code>obj.catch(() =&gt; {})</code>.</p>

<div>{{EmbedInteractiveExample("pages/js/promise-catch.html")}}</div>



<p class="hidden">The source for this interactive example is stored in a GitHub repository. If you'd like to contribute to the interactive examples project, please clone <a href="https://github.com/mdn/interactive-examples">https://github.com/mdn/interactive-examples</a> and send us a pull request.</p>

<p class="hidden">The source for this interactive demo is stored in a GitHub repository. If you'd like to contribute to the interactive demo project, please clone <a href="https://github.com/mdn/interactive-examples">https://github.com/mdn/interactive-examples</a> and send us a pull request.</p>

<h2 id="Sözdizimi">Sözdizimi</h2>

<pre class="syntaxbox"><var>p.catch(onRejected)</var>;

p.catch(function(reason) {
   // rejection
});
</pre>

<h3 id="Parametreler">Parametreler</h3>

<dl>
 <dt>onRejected</dt>
 <dd>A {{jsxref("Function")}} called when the <code>Promise</code> is rejected. This function has one argument:
 <dl>
  <dt><code>reason</code></dt>
  <dd>The rejection reason.</dd>
 </dl>
 The Promise returned by <code>catch()</code> is rejected if <code>onRejected</code> throws an error or returns a Promise which is itself rejected; otherwise, it is resolved.</dd>
</dl>

<h3 id="Dönen_değer">Dönen değer</h3>

<p>Internally calls <code>Promise.prototype.then</code> on the object upon which is called, passing the parameters <code>undefined</code> and the <code>onRejected</code> handler received; then returns the value of that call (which is a {{jsxref("Promise")}}).</p>

<div class="warning">
<p>Note the examples below are throwing instances of <a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error">Error</a>. This is considered good practice in contrast to throwing Strings: Otherwise the part doing the catching would have to make checks to see if the argument was a string or an error, and you might lose valuable information like stack traces.</p>
</div>

<p><strong>Demonstration of the internal call:</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('&gt; &gt; &gt; &gt; &gt; &gt; called .then on %o with arguments: %o', this, arguments);
        return originalThen.apply(this, arguments);
    };
    Promise.prototype.catch = function(){
        console.log('&gt; &gt; &gt; &gt; &gt; &gt; 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:
// &gt; &gt; &gt; &gt; &gt; &gt; called .catch on Promise{} with arguments: Arguments{1} [0: function XXX()]
// &gt; &gt; &gt; &gt; &gt; &gt; called .then on Promise{} with arguments: Arguments{2} [0: undefined, 1: function XXX()]
</pre>

<h2 id="Açıklama">Açıklama</h2>

<p>The <code>catch</code> method can be useful for error handling in your promise composition.</p>

<h2 id="Örnekler">Örnekler</h2>

<h3 id="Using_and_chaining_the_catch_method">Using and chaining the <code>catch</code> method</h3>

<pre class="brush: js">var p1 = new Promise(function(resolve, reject) {
  resolve('Success');
});

p1.then(function(value) {
  console.log(value); // "Success!"
  throw new Error('oh, no!');
}).catch(function(e) {
  console.log(e.message); // "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="Gotchas_when_throwing_errors">Gotchas when throwing errors</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 new Error('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 new Error('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 new Error('Silenced Exception!');
});

p3.catch(function(e) {
   console.log(e); // This is never called
});</pre>

<h3 id="If_it_is_resolved">If it is resolved</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="Specifications">Specifications</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="Tarayıcı_uyumluluğu">Tarayıcı uyumluluğu</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="Ayrıca_bakınız">Ayrıca bakınız</h2>

<ul>
 <li>{{jsxref("Promise")}}</li>
 <li>{{jsxref("Promise.prototype.then()")}}</li>
</ul>