promises in javascript with example
Example 1: 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);
});
};
Example 2: making promises in js
getData()
.then(data => console.log(data))
.catch(error => console.log(error));