js create a promise
/*
A Promise is a proxy for a value not necessarily known when the promise is created.
It allows you to associate handlers with an asynchronous action's eventual success
value or failure reason.
*/
let promise = new Promise((resolve , reject) => {
fetch("https://myAPI")
.then((res) => {
// successfully got data
resolve(res);
})
.catch((err) => {
// an error occured
reject(err);
});
});js promise examples
//Promise to load a file...
//use with openFile(url, fCallback);
//fCallback(fileContents){ //do something with fileContents}
const loadFile = url => {
return new Promise(function(resolve, reject) {
//Open a new XHR
var request = new XMLHttpRequest();
request.open('GET', url);
// When the request loads, check whether it was successful
request.onload = function() {
if (request.status === 200) {
// If successful, resolve the promise
resolve(request.response);
} else {
// Otherwise, reject the promise
reject(Error('An error occurred while loading image. error code:' + request.statusText));
}
};
request.send();
});
};
const openFile = (url, processor) => {
loadFile(url).then(function(result) {
processor(result);
},
function(err) {
console.log(err);
});
};making promises in js
getData()
.then(data => console.log(data))
.catch(error => console.log(error));javascript promises
firstRequest()
.then(function(response) {
return secondRequest(response);
}).then(function(nextResponse) {
return thirdRequest(nextResponse);
}).then(function(finalResponse) {
console.log('Final response: ' + finalResponse);
}).catch(failureCallback);Copyright © 2021 Codeinu
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