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JavaScript Asynchronous Programming with JavaScript Asynchronous JavaScript with Callbacks Async Programming and Callback Functions

Posted by Junior Aidee
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Junior Aidee
Front End Web Development Techdegree Graduate 14,657 Points

Why did we have to write an arrow function for the below?

And what does that function mean and do exactly?

xhr.onload = () => {
    if(xhr.status === 200) {
      let data = JSON.parse(xhr.responseText);
      console.log(data);
    }
Andrea Caputo
Andrea Caputo
2,002 Points
  • In XHR requests, the .onload method executes the block of code inside of it as the webpage loads.
  • Then we have a condition: IF the .status of the request is equal to 200 (a code that indicates that a request was successful), we execute yet another block of code.
  • Since we're getting a JSON file (a specific JS format containing information), we parse it as a .responseText (it returns the text that we receive from the server as we're requesting it).
  • Lastly, we have to decide what to do with this new data; in this case, we just log it to the console.

Hope that was clear :) XHR's aren't the most intuitive thing in the world, mostly because of weird syntax.

1 Answer

Junior Aidee
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Junior Aidee
Front End Web Development Techdegree Graduate 14,657 Points

Thank you very much for the reply, Andrea It makes sense now!