Why Does My Code Fail to Execute Within d3.json() Callback in D3 v5?

Failure to Execute Code Inside d3.json() Callback in D3 v5

In D3 v5, the execution of code within the d3.json() callback often fails. This differs from the behavior in previous versions where the callback was executed as expected.

Cause:

The signature of d3.json() has undergone a change from D3 v4 to v5. In v5, the request is handled using promises rather than callbacks. The second argument to d3.json() is no longer a callback but an optional RequestInit object.

Solution:

To resolve this issue, convert the code within the callback to a callback function passed as an argument to the new .then() method. The code becomes:

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

Error Handling:

Error handling has also been updated in D3 v5. In previous versions, errors were handled using the first parameter of the callback passed to d3.json(). In v5, the promise returned by d3.json() may be rejected to indicate an error. Errors can be captured using the .catch() method.

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

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