Generator.prototype.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

<var>gen</var>.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

Browser compatibility

See also

• function*