Why Is My Code Within the d3.json() Callback Not Executing in D3 v5?

Code Execution Interruption within d3.json() Callback

In D3 v5, code within the d3.json() callback is failing to execute, leaving developers perplexed. This discrepancy has emerged due to significant changes in the signature of d3.json() since D3 v4.

Migration to Promises in D3 v5

D3 v5 has abandonedXMLHttpRequest and adopted the Fetch API, favoring Promises to manage asynchronous requests. Consequently, the second argument to d3.json() is no longer the callback responsible for handling the request. Instead, it serves as an optional RequestInit object. As a result, d3.json() now returns a Promise that can be manipulated using its .then() method.

Revised Code for Handling Asynchronous Requests

To resolve the issue, your code should be modified as follows:

d3.json("/trip_animate/tripData.geojson")
  .then(function(data){
    // Code from your callback goes here...
  });

Error Handling in D3 v5

Error handling has also undergone changes in D3 v5. In earlier versions, errors were reported through the first parameter of the callback passed to d3.json(). However, in D3 v5, the Promise returned by d3.json() will be rejected if an error occurs. This enables the use of vanilla JS error handling mechanisms:

Using Rejection Handler as Second Argument to .then()

d3.json("/trip_animate/tripData.geojson")
  .then(function(data) {
    // Code from your callback goes here...
  }, function(error) {
    // Error handling code here...
  });

Using .catch() to Handle Rejections

d3.json("/trip_animate/tripData.geojson")
  .then(function(data) {
    // Code from your callback goes here...
  })
  .catch(function(error) {
    // Error handling code here...
  });

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