How to get snekfetch results into an object?

问题

I'm writing a discord.js bot and trying to call a weather API using Node.js / snekfetch. The issue is I can't figure out how to just put the data returned from the API into a javascript object. I want to do something like this:

let [country, ...city] = args;
let url = `http://api.openweathermap.org/data/2.5/forecast?q=${city},${country}&units=metric&APPID=${config.weatherID};`;

var weatherObject;
snekfetch.get(url).then(r => weatherObject = r.body);`

but obviously this doesn't work so what am I doing wrong? It seems like it should be insanely simple but I just can't do it. Nothing I've googled has helped since snekfetch doesn't seem to be widely used and I've been completely unable to extrapolate anything I've learned about promises to this scenario.

Edit: To clarify:

snekfetch.get(url).then(r => console.log(r.body));

prints the object exactly as expected to the console, while

snekfetch.get(url).then(r => weatherObject = r.body);
console.log(weatherObject);

prints undefined. Is there something I'm missing with how .then() statements work?

回答1:

.then() statements don't make the program wait for them to be completed, they just execute their code after the Promise they're attached to is resolved.
That means that you can't reliably use the value that has been set inside a Promise, because the code after the Promise will probably be executed before that Promise resolves.

You can either decide to move the rest of the code inside that .then() statement or use async/await.
If you are inside a function, you can declare that as an async function: that allows you to use the await keyword inside it. await makes the program wait for a Promise to resolve, and instead of a Promise it returns the value that you would use in the .then() function.
Here's an example:

// Instead of using this: 
function getResult(args) {
  let [country, ...city] = args;
  let url = `http://api.openweathermap.org/data/2.5/forecast?q=${city},${country}&units=metric&APPID=${config.weatherID};`;

  var weatherObject;
  snekfecth.get(url).then(response => {
    weatherObject = response.body;
  });

  return weatherObject; // undefined :(
}

// You could write it like this:
async function getResult(args) {
  let [country, ...city] = args;
  let url = `http://api.openweathermap.org/data/2.5/forecast?q=${city},${country}&units=metric&APPID=${config.weatherID};`;

  let response = await snekfecth.get(url);
  var weatherObject = response.body;

  return weatherObject; // right value
}

来源：https://stackoverflow.com/questions/54139035/how-to-get-snekfetch-results-into-an-object