Агуулга
async function myFunction() {
return "Hello";
}
Is the same as:
async function myFunction() {
return Promise.resolve("Hello");
}
Here is how to use the Promise:
myFunction().then(
function(value) { /* code if successful */ },
function(error) { /* code if some error */ }
);
Example #
async function myFunction() {
return "Hello";
}
myFunction().then(
function(value) {myDisplayer(value);},
function(error) {myDisplayer(error);}
);
Or simpler, since you expect a normal value (a normal response, not an error):
Example #
async function myFunction() {
return "Hello";
}
myFunction().then(
function(value) {myDisplayer(value);}
);
let value = await promise;
async function myDisplay() {
let myPromise = new Promise(function(myResolve, myReject) {
myResolve("I love You !!");
});
document.getElementById("demo").innerHTML = await myPromise;
}
myDisplay();
Waiting for a Timeout #
async function myDisplay() {
let myPromise = new Promise(function(myResolve, myReject) {
setTimeout(function() { myResolve("I love You !!"); }, 3000);
});
document.getElementById("demo").innerHTML = await myPromise;
}
myDisplay();
Waiting for a File #
async function getFile() {
let myPromise = new Promise(function(myResolve, myReject) {
let req = new XMLHttpRequest();
req.open('GET', "mycar.html");
req.onload = function() {
if (req.status == 200) {myResolve(req.response);}
else {myResolve("File not Found");}
};
req.send();
});
document.getElementById("demo").innerHTML = await myPromise;
}
getFile();
Browser Support #
ECMAScript 2017 introduced the JavaScript keywords async
and await
.
The following table defines the first browser version with full support for both:
Chrome 55 | Edge 15 | Firefox 52 | Safari 11 | Opera 42 |
Dec, 2016 | Apr, 2017 | Mar, 2017 | Sep, 2017 | Dec, 2016 |