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Promise.prototype.catch()

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El método catch() retorna una Promise y se encarga solo de los casos rejected. Se comporta igual que al llamar Promise.prototype.then(undefined, onRejected) (de hecho, al llamar obj.catch(onRejected) internamente llama a 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).

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.
Draft  

Browser compatibility

FeatureChromeFirefoxEdgeInternet ExplorerOperaSafari
Soporte básico32.029.0(Si)(No)197.1
FeatureAndroidChrome for AndroidEdge mobileFirefox for AndroidIE mobileOpera AndroidiOS Safari
Soporte básico4.4.432.0(Si)29(No)(Si)8.0

See also

Etiquetas y colaboradores del documento

 Colaboradores en esta página: walbuc
 Última actualización por: walbuc,