Generator.prototype.throw()
Baseline Widely available
This feature is well established and works across many devices and browser versions. It’s been available across browsers since September 2016.
The throw()
method of Generator
instances acts as if a throw
statement is inserted in the generator's body at the current suspended position, which informs the generator of an error condition and allows it to handle the error, or perform cleanup and close itself.
Syntax
generatorInstance.throw(exception)
Parameters
Return value
If the thrown exception is caught by a try...catch
and the generator resumes to yield more values, it will return an Object
with two properties:
Exceptions
If the thrown exception is not caught by a try...catch
, the exception
passed to throw()
will be thrown out from the generator function.
Description
The throw()
method, when called, can be seen as if a throw exception;
statement is inserted in the generator's body at the current suspended position, where exception
is the exception passed to the throw()
method. Therefore, in a typical flow, calling throw(exception)
will cause the generator to throw. However, if the yield
expression is wrapped in a try...catch
block, the error may be caught and control flow can either resume after error handling, or exit gracefully.
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
Specification |
---|
ECMAScript Language Specification # sec-generator.prototype.throw |
Browser compatibility
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