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.




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.
Any JavaScript value returned by the iterator. Can be omitted when done is true.


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!');

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


ECMAScript (ECMA-262)
The definition of 'Generator.prototype.throw' in that specification.

Browser compatibility

Update compatibility data on GitHub
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidFirefox for AndroidOpera for AndroidSafari on iOSSamsung InternetNode.js
throwChrome Full support 39Edge Full support 13Firefox Full support 26IE No support NoOpera Full support 26Safari Full support 10WebView Android Full support 39Chrome Android Full support 39Firefox Android Full support 26Opera Android Full support 26Safari iOS Full support 10Samsung Internet Android Full support 4.0nodejs Full support 4.0.0
Full support 4.0.0
Full support 0.12
Disabled From version 0.12: this feature is behind the --harmony runtime flag.


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User must explicitly enable this feature.

See also