Using Promise.all with Async/Await to get data from multiple endpoints

Sometimes you want to get some data from several different API endpoints. In this example I will be using the Star Wars API to get information about some characters. See below.

const urls = [
  "https://swapi.co/api/people/1",
  "https://swapi.co/api/people/2",
  "https://swapi.co/api/people/3",
  "https://swapi.co/api/people/4",
]

Begin with an outline for the function. Do this so you can easily visualise what's happening. I use a try/catch block as it’s easily to see what’s going on.

Try/Catch

• Try - ‘Do this.’
• Catch - ‘Can’t do the try? Then do this instead.

const fetchData = async () => {
  try {
  } catch (error) {}
}

For this the catch block will console log the error with a message if the try fails.

const fetchData = async () => {
  try {

  } catch (error) {
    console.log(‘ERROR’, error)
  }
}

The serious business happens in the try block below.

const fetchData = async () => {
  try {
    const response = await Promise.all(urls.map(url => fetch(url)))
    console.log(response)
  } catch (error) {
    console.log("Error", error)
  }
}

• We create a variable response for holding our data.
• Using the keyword await’. Await - ‘Go do this for me and come back.’
• Promise.all method is used to tell the function to go and do all of the urls from our urls array. One at a time.
• Using .map() array method to iterate over our array.
• We then pass each url into the fetch(). Seen as url => fetch(url)

Logging the response you will see the promises have been fulfilled. Each url is hit. However we want the data in a format we can use. So there's one last thing to do. We must make the response a JSON object.

const fetchData = async () => {
  try {
    const response = await Promise.all(
      urls.map(url => fetch(url).then(res => res.json()))
    )
    console.log(response)
  } catch (error) {
    console.log("Error", error)
  }
}

Notice above we added .then(res => res.json(). We use .then for chaining. Taking the response or 'res' which is returned once 'fetched'. Convert the response to JSON which we can use.

Code for you to try

const urls = [
  "https://swapi.co/api/people/1",
  "https://swapi.co/api/people/2",
  "https://swapi.co/api/people/3",
  "https://swapi.co/api/people/4",
]

const fetchData = async () => {
  try {
    const response = await Promise.all(
      urls.map(url => fetch(url).then(res => res.json()))
    )
    console.log(response)
  } catch (error) {
    console.log("Error", error)
  }
}
fetchData()

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