TypeError: object async_generator can’t be used in ‘await’ expression
This error message is related to the usage of the ‘await’ keyword in an invalid context with an ‘async_generator’ object in JavaScript.
To understand this error, let’s look at an example:
async function* exampleGenerator() {
yield 1;
yield 2;
yield 3;
}
async function exampleAsyncFunction() {
const generator = exampleGenerator();
await generator; // This line causes the error
}
exampleAsyncFunction()
.then(() => console.log("Done"))
.catch((error) => console.error(error));
In the above example, we have an asynchronous generator function called ‘exampleGenerator’ that yields some values. Inside the ‘exampleAsyncFunction’, we create an instance of the generator using ‘exampleGenerator()’ and store it in the ‘generator’ variable.
The problematic line is ‘await generator’. The intention here might be to await each yielded value from the generator, but the generator itself cannot be directly awaited. This is what causes the ‘TypeError: object async_generator can’t be used in ‘await’ expression’.
To fix this error, we need to iterate over the generator and await each yielded value. Here’s an updated version of the example with a proper usage of ‘for await…of’ loop:
async function* exampleGenerator() {
yield 1;
yield 2;
yield 3;
}
async function exampleAsyncFunction() {
const generator = exampleGenerator();
for await (const value of generator) {
console.log(value); // Process each yielded value
}
}
exampleAsyncFunction()
.then(() => console.log("Done"))
.catch((error) => console.error(error));
In the updated version, we use the ‘for await…of’ loop to iterate over the generator. This loop automatically awaits each yielded value and assigns it to the ‘value’ variable, allowing us to process the values correctly without triggering the error.
I hope this explanation helps you understand the ‘TypeError: object async_generator can’t be used in ‘await’ expression’ error and how to fix it.