d3.json() loads a JSON file and converts its contents into JavaScript data, typically an array of objects. JSON stores data as key-value pairs, making fields accessible through JavaScript dot notation. section 3.1.3
Load data before building a visualization
Because loading external data is asynchronous, wait for the complete dataset before manipulating it or creating marks: d3.json("data.json").then(data => { /* measure, reorganize, and visualize data */ }). The then() callback receives the entire loaded dataset; loading callbacks can also support type conversion and other data manipulation. section 3.6 section 3.1.3
[
{
id": 1,
"name": "Zoe",
"position": "Data analyst",
"works_with_d3": false
},
{
"id": 2,
"name": "James",
"position": "Frontend developer",
"works_with_d3": true
},
{
"id": 3,
"name": "Alice",
"position": "Fullstack developer",
"works_with_d3": true
},
{
"id": 4,
"name": "Hubert",
"position": "Designer",
"works_with_d3": false
}
]
Use the JSON array of objects to inspect the key-value structure returned by a typical dataset. section 3.1.3
Use d3.json() with these practical rules:
- Wait for data availability before accessing fields or generating visualization elements. section 3.6
- Check numeric formatting and use the loading callback for type conversion or other preparation. section 3.6
