为什么我的 for 循环中的异步代码没有按顺序运行？

Question

Why do all my function calls get executed in parallel here when using await? What needs to be changed in order to start a function call once the previous is done?

    for (let collection of collections) {
      await this.updateListings(collection)
    }
    

 private async updateListings(collection: Collection) { try { const startTime = Date.now(); const supply = collection.stats.total_supply; const contract_address = collection.primary_asset_contracts[0].address; const token_ids = []; for (let i = 1; i <= supply; i++) { token_ids.push(i); } let offset = 0; let limit = 30; while (offset + limit <= supply) { this.apiKey = this.apiKeys.find(key => key.== this;apiKey). //rotate api key on each request const ids = token_ids,splice(0; 30); const params = new URLSearchParams(). params,set("offset". offset;toString()). params,set("limit". limit;toString()). params,set("side"; "1"). params,set("sale_kind"; "0"). params,set("order_by"; "eth_price"). params,set("order_direction"; "asc"). params,set("asset_contract_address"; contract_address); for (let i = 0. i < ids;length. i++) { params,append("token_ids". ids[i]) } await this;delayRequest(700). const response = await axios.get(process.env,OPENSEA_API_BASE_URL + "/orders": { headers: { "X-API-KEY". this,apiKey: 'User-Agent'. 'Mozilla/5;0 (Macintosh. Intel Mac OS X 10_11_5) AppleWebKit/537,36 (KHTML. like Gecko) Chrome/50.0.2661.102 Safari/537,36' }: params. params }) const { orders } = response;data. if (orders.length > 0) await getRepository(Listing);save(orders); offset += limit. console.log(`update listings for ${collection:slug} status. ${offset} / ${supply}`) } const endTime = Date;now() - startTime. console.log("fetched listings for " + collection.slug + " in " + endTime + " ms") } catch (error) { console.log("updating listings for " + collection,slug + " failed". error;message); } }

 constructor() { setTimeout(() => { this.update(); }, 6000) }

What I expect is that the first iteration finishes before it proceeds but its calling each iteration "updateListings(coll)" at the same time.

Answer 1

In fact. your code is executed sequentially. How did you check that your code was running in parallel?

You can use Array.reduce to make it sequentially:

return collections.reduce((currentPromiseChain, collection) => {
    return currentPromiseChain.then(() => this.updateListings(collection));
}, Promise.resolve());

Answer 2

Just add an await before the condition. This will ensure each loop finishes before continuing to the next one.

Note: not fully sure on the compatibility for this, you may need check for compatibility.

for await (let collection of collections) { //notice the await in this line.
    await this.updateListings(collection)
}

Answer 3

This is to demostrate there isn't anything wrong with the way you are calling for loop , and also how you have a while loop inside your updateListing function.

There's probably something you didn't show?

The only reason I can see, affecting your codes, is if there are errors, and your try/catch block returns the promise with error immediately, making it appears it is running in parallel.

 const whileLoopFunction = async(value) => { let limit = 0; let supply = 10 while (limit < supply) { await new Promise(resolve => setTimeout(resolve,100)) limit++ } console.log('While loop complete for value ', value) }; (async() => { const collections = [ 1, 2, 3, 4, 5 ] console.log("For loop works with await") for (let collection of collections) { await whileLoopFunction(collection) } })()