I use fetch to get data for each element of an array. Those values are pushed into an array and I want to return the max of those values once all values are fetched.
For that I used a promise:
async function init() {
await maxWaste(nut0Codes).then(response => {
console.log(response);
});
}
function maxWaste(nutCodes) {
return new Promise(resolve => {
let waste = [];
nutCodes.forEach((element) => {
let query = queryMaxWaste(element);
fetch(address + encodeURIComponent(query))
.then(response => {
return response.json();
})
.then(response => {
waste.push(response.results.bindings[0].wasteGeneration.value);
console.log(waste);
});
});
let maxWaste = Math.max(waste);
resolve(maxWaste);
});
}
I am not sure where my mistake is but the resolve happens before the fetch is done :
I receive the zero from the console.log(response)
and I don't know why it is not working.
Any advice would be appreciated!
If you're going to write code that uses async
, you should actually leverage async
. If this needs to be run synchronously-ish, you can await within a for loop. If you want them all to run simultaneously, use a map
and Promise.all
.
async function init() {
const response = await maxWaste(nut0Codes);
console.log(response);
}
async function maxWaste(nutCode) {
const waste = [];
for (const element in nutCode) {
const query = queryMaxWaste(element);
const response = await fetch(address + encodeURIComponent(query));
const json = await response.json();
waste.push(json.results.bindings[0].wasteGeneration.value);
console.log(waste);
}
const maxWaste = Math.max(waste);
return maxWaste;
}
You could also try writing it like this so that you don't wait for each response to complete before running the next fetch
:
async function init() {
const response = await maxWaste(nut0Codes);
console.log(response);
}
async function maxWaste(nutCode) {
const waste = await Promise.all(nutCode.map(async element => {
const query = queryMaxWaste(element);
const response = await fetch(address + encodeURIComponent(query));
const json = await response.json();
return json.results.bindings[0].wasteGeneration.value;
}));
return Math.max(waste);
}
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