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

Code within d3.json() Callback Not Executed

Explanation

In D3 v5, the signature of d3.json() has changed significantly compared to its previous versions. Instead of using a callback function, d3.json() now returns a Promise that can be handled using its .then() method. This change addresses several issues with the old implementation and brings D3 in line with modern browser APIs.

Solution

To fix the issue where code within the d3.json() callback is not executed, you need to update your code to use Promises. The new syntax for loading data from a GeoJSON file is as follows:

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

Handling Errors

In addition to changing the callback structure, D3 v5 also introduces new ways to handle errors when loading data. Instead of passing an error handler as the first parameter to the callback function, you should use the .catch() method of the Promise:

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

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