AsyncGenerator.prototype.throw()
The throw()
method of AsyncGenerator
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
js
asyncGeneratorObject.throw(exception)
Parameters
exception
-
The exception to throw. For debugging purposes, it is useful to make it an
instanceof
Error
.
Return value
If the thrown error is not caught, it will return a Promise
which rejects with the exception passed in.
If the exception is caught by a try...catch
and the generator resumes to yield more values, it will return a Promise
which resolves with an Object
with two properties:
done
-
A boolean value:
true
if the generator function's control flow has reached the end.false
if the generator function is able to produce more values.
value
-
The value yielded from the next
yield
expression.
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.
js
// An async task. Pretend it's doing something more useful
// in practice.
function sleep(time) {
return new Promise((resolve, reject) => {
setTimeout(resolve, time);
});
}
async function* createAsyncGenerator() {
while (true) {
try {
await sleep(500);
yield 42;
} catch (e) {
console.error(e);
}
}
}
const asyncGen = createAsyncGenerator();
asyncGen.next(1).then((res) => console.log(res)); // { value: 42, done: false }
asyncGen
.throw(new Error("Something went wrong")) // Error: Something went wrong
.then((res) => console.log(res)); // { value: 42, done: false }
Specifications
Specification |
---|
ECMAScript Language Specification # sec-asyncgenerator-prototype-throw |
Browser compatibility
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