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generator.throw

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!');
    }
  }
}

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

Specifications

Browser compatibilityUpdate compatibility data on GitHub

Desktop
Chrome Edge Firefox Internet Explorer Opera Safari
throw 39 13 26 No 26 10
Mobile
Android webview Chrome for Android Firefox for Android Opera for Android Safari on iOS Samsung Internet
throw 39 39 26 26 10 4.0
Server
Node.js
throw 4.0.0
4.0.0
0.12
Disabled
Disabled From version 0.12: this feature is behind the --harmony runtime flag.

See also

© 2005–2018 Mozilla Developer Network and individual contributors.
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://wiki.developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Generator/throw