The catch() method returns a Promise and deals with rejected cases only. It behaves the same as calling Promise.prototype.then(undefined, onRejected) (in fact, calling obj.catch(onRejected) internally calls obj.then(undefined, onRejected)).

Syntax

p.catch(onRejected);

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

Parameters

onRejected
A Function called when the Promise is rejected. This function has one argument:
reason
The rejection reason.
The Promise returned by catch() is rejected if onRejected throws an error or returns a Promise which is itself rejected; otherwise, it is resolved.

Return value

Internally calls Promise.prototype.then on the object upon which is called, passing the parameters undefined and the onRejected handler received; then returns the value of that call (which is a Promise).

The examples below are throwing strings. This is considered bad practice. Always throw an instance of Error. 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

Demonstration of the internal call:

// 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()]

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.
Living Standard  

Browser compatibility

FeatureChromeEdgeFirefoxInternet ExplorerOperaSafari
Basic support32 Yes29 No198
FeatureAndroid webviewChrome for AndroidEdge mobileFirefox for AndroidIE mobileOpera AndroidiOS Safari
Basic support4.4.432 Yes29 No Yes8

See also

Document Tags and Contributors

 Last updated by: NigelKibodeaux,