The catch() method returns a Promise
and deals with rejected cases only. It behaves the same as calling Promise.prototype.then(undefined, onRejected)
.
Syntax
p.catch(onRejected); p.catch(function(reason) { // rejection });
Parameters
- onRejected
- A
Function
called when thePromise
is rejected. This function has one argument:reason
- The rejection reason.
catch()
is rejected ifonRejected
throws an error or returns a Promise which is itself rejected; otherwise, it is resolved.
Return value
A Promise
.
Description
The catch
method can be useful for error handling in your promise composition.
Examples
Using and chaining the catch
method
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'); });
Gotchas when throwing errors
// 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 });
If it is resolved
//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); });
Specifications
Specification | Status | Comment |
---|---|---|
ECMAScript 2015 (6th Edition, ECMA-262) The definition of 'Promise.prototype.catch' in that specification. |
Standard | Initial definition in an ECMA standard. |
ECMAScript Latest Draft (ECMA-262) The definition of 'Promise.prototype.catch' in that specification. |
Draft |
Browser compatibility
To contribute to this compatibility data, please write a pull request against this file: https://github.com/mdn/browser-compat-data/blob/master/javascript/promise.json.
No compatibility data found. Please contribute data for "javascript/promise" to the MDN compatibility data repository.
See also
Document Tags and Contributors
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ParaBolt,
SheltonDong,
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Granjow,
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realityking
Last updated by:
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