How to Load Data from CSV Files in D3 v5 with Promises?

Loading Data from CSV Files in D3 v5

In D3 v4, loading data from CSV files was straightforward using XMLHttpRequest. However, with the introduction of Promises in D3 v5, the process has changed slightly.

Using D3 v5

To load data from a CSV file using D3 v5, you can utilize the fetch() API. Here's how you can modify your code:

d3.csv('data/dataset.csv')
    .then(function(data) {
        if (error !== null) {
            alert ("Couldn't load the dataset!");
        } else {
            //do something
        };
    })
    .catch(function(error) {
        //handle error
    })

Understanding the Difference

The key difference between D3 v4 and D3 v5 lies in how they handle asynchronous requests. D3 v4 uses XmlHttpRequest, which doesn't return a Promise. As a result, you pass it a callback function that runs once the request is complete.

In contrast, D3 v5 uses the Promise API, which allows you to handle the success and failure cases separately. The 'then()' function is used to handle the success case, while 'catch()' is for handling errors.

Example

The following code snippet provides a complete example of how to load data from a CSV file using D3 v5:

d3.csv('yourcsv.csv')
  .then(function(data) {
      // data is now whole data set
      // draw chart in here!
  })
  .catch(function(error){
     // handle error   
  })

By leveraging the Promise API, D3 v5 provides a more structured and flexible way to handle asynchronous data loading compared to D3 v4.

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