CODEWITHSUNDEEP
javascriptnode.jsasync-await
I'll-Be-Back
I'll-Be-Back

Reputation: 10828

Class - return data via await?

I am learning how to use class with Async/Await. I think I am doing something wrong with getData function in the Run class.

It should output "Hello World" when using await get() (experiment).

When I run the script, I get an error:

UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 1)

Class Script:

class Run {
    constructor() {
        this.stop = false;
    }

    async getData(entry) {
        if (this.stop) {
            console.log("Stopped")
            return;
        }

        return await this.get();
    }

    async get() {
        return "Hello World";
    }

    stop() {
        this.stop = true;
    }
}

Usage:

let run =  new Run();

run.getData(async (entry) => { 
    console.log(entry);
});

Upvotes: 0

Views: 54

Answers (2)

Pete Houston
Pete Houston

Reputation: 15079

Your original code refer to the other methods, not the one in your class:

async getData(entry) {
    if (stop) {  // <--- this refers to this.stop() method
        console.log("Stopped")
        return;
    }

    return await get(); <--- this doesn't refer to your `this.get()` method
}

So, add this. to fix it at above two positions.

Upvotes: 0

Kim Kern
Kim Kern

Reputation: 60347

You're getting an error because you forgot the this qualifier:

async getData(entry) {
    if (this.stop) {
        ^^^^

Using return await only makes sense, when you use it within a try/catch block. Otherwise, it is completely redundant.

You should use it here instead. Also, getData does not use its parameter entry. You should call it directly:

console.log(await run.getData());
            ^^^^^

Upvotes: 1

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