Combining two promises using promise.all

In addition to existing answers, this is when async..await becomes useful, since it's already used in other functions. The array that Promise.all resolves to can be destructured:

async loadWeather(lat, lon) {  const [address, forecast] = await Promise.all([    API.getAddress(lat, lon),    API.getForecast(lat, lon)  ]);  this.address = address.name;  this.forecast = forecast;}

First, decide if you want the promise to fail if any of the two API calls fail. Promise.all will fail in this case, Promise.allSettled will not. It depends on what you want for your app.

To combine, you can do the following:

loadWeather(lat, lon) {  Promise.all([    API.getAddress(lat, lon),    API.getForecast(lat, lon)  ]).then(([addressResult, forecastResult]) => {    this.address = addressResult.name;    this.forecast = forecastResult;  });}

Promise.all returns an array of results. This makes sense if you consider that you pass it an array of promises.

Yes, you can write

loadWeather(lat, lon) {  Promise.all([    API.getAddress(lat, lon),    API.getForecast(lat, lon),  ]).then(([addressResult, forecastResult]) => {    this.address = addressResult.name;    this.forecast = forecastResult;  });}

However, it doesn't really seem necessary, as both functions handle errors already and there doesn't seem to be a reason why the property assignments would need to wait for both promises to fulfill.