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promise-race.html
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<!DOCTYPE html>
<html>
<head>
<title>Javascript Promise Race</title>
</head>
<body>
<h2>Javascript Promise Race</h2>
<p>The Promise.race() method returns a promise that fulfills or rejects as soon as one of the promises in an iterable fulfills or rejects, with the value or reason from that promise.</p>
<script>
let urls = [
'https://jsonplaceholder.typicode.com/users',
'https://jsonplaceholder.typicode.com/posts/1'
];
const promise1 = new Promise((resolve, reject) => {
const request = new XMLHttpRequest();
request.open('GET', urls[0]);
request.onload = () => {
if (request.status === 200) {
resolve(request.response); // we got data here, so resolve the Promise
} else {
reject(Error(request.statusText)); // status is not 200 OK, so reject
}
};
request.onerror = () => {
reject(Error('Error fetching data.')); // error occurred, reject the Promise
};
request.send(); // send the request
});
const promise2 = new Promise((resolve, reject) => {
const request = new XMLHttpRequest();
request.open('GET', urls[1]);
request.onload = () => {
if (request.status === 200) {
resolve(request.response); // we got data here, so resolve the Promise
} else {
reject(Error(request.statusText)); // status is not 200 OK, so reject
}
};
request.onerror = () => {
reject(Error('Error fetching data.')); // error occurred, reject the Promise
};
request.send(); // send the request
});
/* The Promise.race() method returns a promise that fulfills or rejects as soon as
one of the promises in an iterable fulfills or rejects, with the value or reason from that promise. */
Promise.race([promise1, promise2]).then(responses => {
// respose will get in string format. JSON.parse is used to convert string to JSON format
console.log('Promise Race responses => ', typeof(responses), JSON.parse(responses));
});
</script>
</body>
</html>