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QUESTION
Why on printing I get value of null from API call in Loop
Asked 2022-Apr-16 at 03:06COIN LIST is an array of crypto coins(["BTCUSDT",...]). I try to get the price using getPriceAction and RSI from getRSI and these two functions are working when I try to console DATA. But when I try to print the response after the completion of the loop. It prints the empty array and the length is 0 of this array. I want to store the DATA object (consisting of SYMBOL, closing price and RSI) as an element in the response array
import { COIN_LIST } from "./COIN_LIST.js";
import { getPriceAction } from "./PRICE_ACTION.js";
import { getRSI } from "./RSI.js";
async function main() {
try {
let response = await [];
await COIN_LIST.forEach((element, i) => {
setTimeout(() => {
let data = { symbol: element };
getPriceAction(element, "4h").then((res) => {
data.closingPrice = res;
getRSI(res).then((res) => {
data.RSI = res.reverse();
data.closingPrice = data.closingPrice.reverse();
response.push(data);
console.log(data)
});
});
}, i * 1000);
});
console.log(response);
} catch (error) {
console.log(error.message);
}
}
main();
ANSWER
Answered 2022-Apr-16 at 02:43After the completion of the loop, the promises didn't get resolved yet, that's why it print an empty array.
One way to achieve what you need is using await for(...)
, or wait for all promises to be resolved, and then print the results.
import { COIN_LIST } from "./COIN_LIST.js";
import { getPriceAction } from "./PRICE_ACTION.js";
import { getRSI } from "./RSI.js";
async function main() {
try {
let response = []; //---> don't need that `await`
const promises = []; //---> array of promises
COIN_LIST.forEach((element, i) => {
setTimeout(() => {
let data = { symbol: element };
const promise = getPriceAction(element, "4h").then((res) => {
data.closingPrice = res;
getRSI(res).then((res) => {
data.RSI = res.reverse();
data.closingPrice = data.closingPrice.reverse();
response.push(data);
console.log(data)
});
});
promises.push(promise) //---> save the reference to a promise
}, i * 1000);
});
await Promise.all(promises) //---> await for all promises to be resolved, then print the result
console.log(response);
} catch (error) {
console.log(error.message);
}
}
main();
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