The throw() method resumes the execution of a generator by throwing an error into it and returns an object with two properties done and value.

Syntax

gen.throw(exception)

Parameters

exception
The exception to throw. For debugging purposes, it is useful to make it an instanceof Error.

Return value

An Object with two properties:

  • done (boolean)
    • Has the value true if the iterator is past the end of the iterated sequence. In this case value optionally specifies the return value of the iterator.
    • Has the value false if the iterator was able to produce the next value in the sequence. This is equivalent of not specifying the done property altogether.
  • value - any JavaScript value returned by the iterator. Can be omitted when done is true.

Examples

Using throw()

The following example shows a simple generator and an error that is thrown using the throw method. An error can be caught by a try...catch block as usual.

function* gen() {
  while(true) {
    try {
       yield 42;
    } catch(e) {
      console.log('Error caught!');
    }
  }
}

var g = gen();
g.next();
// { value: 42, done: false }
g.throw(new Error('Something went wrong'));
// "Error caught!"
// { value: 42, done: false }

Specifications

Specification Status Comment
ECMAScript 2015 (6th Edition, ECMA-262)
The definition of 'Generator.prototype.throw' in that specification.
Standard Initial definition.
ECMAScript Latest Draft (ECMA-262)
The definition of 'Generator.prototype.throw' in that specification.
Draft  

Browser compatibility

Update compatibility data on GitHub
DesktopMobileServer
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidEdge MobileFirefox for AndroidOpera for AndroidiOS SafariSamsung InternetNode.js
Basic supportChrome Full support 39Edge Full support 13Firefox Full support 26IE No support NoOpera Full support YesSafari Full support 10WebView Android Full support YesChrome Android Full support YesEdge Mobile Full support 13Firefox Android Full support 26Opera Android Full support YesSafari iOS Full support 10Samsung Internet Android Full support Yesnodejs Full support 4.0.0
Full support 4.0.0
Full support 0.12
Disabled
Disabled From version 0.12: this feature is behind the --harmony runtime flag.

Legend

Full support  
Full support
No support  
No support
User must explicitly enable this feature.
User must explicitly enable this feature.

See also

Document Tags and Contributors

Contributors to this page: fscholz, jameshkramer, nmve, kdex, David_Gilbertson, stasm
Last updated by: fscholz,