Jeanluca Scaljeri Jeanluca Scaljeri - 6 months ago 25
Javascript Question

async / await not working in combination with fetch

I'm trying to use ES7

async
/
await
together with
fetch
. I know I'm close but I can't get it to work. Here is the code:

class Bar {
async load() {
let url = 'https://finance.yahoo.com/webservice/v1/symbols/goog/quote?format=json';
try {
response = await fetch(url);
return response.responseText;
} catch (e) {
return e.message;
}
}
}


which I use as follows:

let bar = new Bar();
bar.load().then(function (val) {
console.log(val);
});


DEMO

For some reason I always get into the
catch
with the message

response is not defined


Any suggestions what I do wrong ?

UPDATE: As suggested in the comments, it might be an issue with
fetch
, so I tried a simplified (ES5) version:

<!doctype html>

<html>
<head>
<script>
var url = 'https://finance.yahoo.com/webservice/v1/symbols/goog/quote?format=json';
fetch(url, {method: 'get', mode: 'cors'}).then(function (response) {
console.log(response.responseText);
});
</script>
<head>

<body></body>
<html>


And still doesn't work :( However, if I replace fetch it works:

var request = new XMLHttpRequest();
request.open("GET", url, false);
request.send(null);
console.log(request.responseText);

Answer

You forgot to declare response as a variable. Class code is always strict code, and you won't get away with assigning to implictly global variables. Instead, it throws a ReferenceError.

Apart from that, Response objects don't have a responseText property like a XHR, they do have a .text() method that waits for the body to be received and returns a promise.

class Bar {
    async load() {
        let url =  'https://finance.yahoo.com/webservice/v1/symbols/goog/quote?format=json';
        try {
            let response = await fetch(url);
//          ^^^^
            return await response.text();
//                                ^^^^^^
        } catch (e) {
            return e.message;
        }
    }
}