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There is a question about for await ... of loop.

I have the following code:

    for await (let V of reagentItems.map(objectElement => getPricing(objectElement))) {
       console.log(objectElement) //I'd like to have access to the current iteration.
       //or
       console.log(reagentItems[i]) //current fulfilled element from reagent.map
    }

So the problem is that this array (from .map) of functions (V as a single response of getPricing) doesn't return the objectElement itself but I need to have access to this objectElement inside for await ... of loop.

Does it possible somehow or not? And if it doesn't, using of Promise.all handles this problem somehow? Or I should modify the original getPricing and return current objectElement with other results?

There is a question about for await ... of loop.

I have the following code:

    for await (let V of reagentItems.map(objectElement => getPricing(objectElement))) {
       console.log(objectElement) //I'd like to have access to the current iteration.
       //or
       console.log(reagentItems[i]) //current fulfilled element from reagent.map
    }

So the problem is that this array (from .map) of functions (V as a single response of getPricing) doesn't return the objectElement itself but I need to have access to this objectElement inside for await ... of loop.

Does it possible somehow or not? And if it doesn't, using of Promise.all handles this problem somehow? Or I should modify the original getPricing and return current objectElement with other results?

• javascript
• node.js
• for-loop
• async-await

Share Improve this question Follow edited Oct 15, 2022 at 9:21 AlexZeDim asked Apr 19, 2020 at 14:46 AlexZeDimAlexZeDim 4,37244 gold badges3434 silver badges7777 bronze badges 3

• 1 I'd remend you split the question into the actual two questions it contains. – fjc Commented Apr 19, 2020 at 15:08
• What exactly does getPricing return? A Promise? – fjc Commented Apr 19, 2020 at 15:13
• an object like {item_id: Number, price: Number, ... } but this data from this object received via async/await functions, and getPricing doesn't return the object_element itself. So the question is all about: «Can I access the current_executed element/index from Array of functions» – AlexZeDim Commented Apr 19, 2020 at 15:15

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2 Answers 2

Sorted by: Reset to default 1

From what I can understand from your question and your ments, you want to be able to access both object_element and the result of getPricing(object_element) within the for loop.

Your problem right now is that as a result of map, you only have the result of getPricing, but not the original object_element. As a solution, simply return both from map in an object:

// just a random getPricing function
function getPricing(objectElement) {
    return {
        item_id: objectElement.id,
        price: Math.random()
    };
}

const reagent_items = [
    {
        id: 'a'
    },
    {
        id: 'b'
    }
];

for (let V of reagent_items.map(object_element => ({object_element, pricing: getPricing(object_element)}))) {
    console.log(`object_element: ${JSON.stringify(V.object_element)}, pricing: ${JSON.stringify(V.pricing)}`);
}

You should not be using for await here at all - that is meant for asynchronous generators. Instead, do

for (const object_element of reagent_items) {
    const V = await getPricing(object_element);
    console.log(object_element, V)
    …
}

With Promise.all, the code would look like this:

Promise.all(reagent_items.map(object_element =>
    getPricing(object_element).then(V => {
        console.log(object_element, V);
        …
    })
)).then(…)

// or:

await Promise.all(reagent_items.map(async object_element => {
    const V = await getPricing(object_element)
    console.log(object_element, V);
    …
}));

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