Wait for data from external API before making POST request - node.js

Question

I'm using the IBM Watson Tone Analyser API with Express.js and React. I have this code which sends some test to the Watson API:
// tone-analyser.js
class ToneAnalysis {
constructor() {
const params = {
username: process.env.USERNAME,
password: process.env.PASSWORD,
version_date: '2018-01-31'
}
this.Analyzer = new ToneAnalyzerV3(params);
}
ToneAnalyser(input) {
let tones = this.Analyzer.tone(input, (err, tone) => {
if (err) console.log(err.message)
let voiceTone = tone.document_tone.tones[0].tone_id;
console.log(voiceTone) // Logs the right value on Node.js console
return voiceTone;
});
return tones;
}
}
module.exports = ToneAnalysis;
I then use this on my Express backend like so:
// server.js
const ToneAnalysis = require('./api/tone-analyser');
const app = express();
const input = {
tone_input: 'I am happy',
content_type: 'text/plain'
}
app.get('/api/tone', (req, res) => {
let tone = new ToneAnalysis().ToneAnalyser(input);
return res.send({
tone: tone
});
});
And I make an API call from React here:
// App.js
componentDidMount() {
this.callApi()
.then(res => {
console.log(res.tone); // Logs the wrong value on Chrome console
})
.catch(err => console.log(err));
}
callApi = async () => {
const response = await fetch('/api/tone');
const body = await response.json();
if (response.status !== 200) throw new Error(body.message);
console.log(body);
return body;
};
I expect the value of res.tone to be a string showing the tone gotten from the tone analysis function (new ToneAnalysis().ToneAnalyser(input);). Instead, I get
{
uri: {...},method: "POST", headers: {...}}
headers: {...},
uri: {...},
__proto__: Object
}
I think this happens because the res.send(...) runs before tone has a value from the API. My question is, how do I make res.send(...) run only after tone has a value?
I tried wrapping the callback function in this.Analyzer.tone(input, [callback]) in an async/await block, but that did not fix the issue. Any ideas on how to fix this will be highly appreciated. Thanks!

Answer 1

If the call to
let tone = new ToneAnalysis().ToneAnalyser(input);
returns a promise then you could do something like
tone.then(res.send.bind(res))

Answer 2

If the call to
let tone = new ToneAnalysis()`enter code here`.ToneAnalyser(input);
returns a promise then you could do something like
tone.then(res.send.bind(res))