问题
I try to load data from two different sources. After loading the data I want to use it within a riot tag file. But I do not understand how to load the second file, because I do not really understand the asynchronous call.
What do I have to modify in my code to get the data? Right now, the second data object is undefined. Here is my code:
import { csv, json } from 'd3-fetch'
csv('/data/stations.csv', function (stations) {
json('data/svg_data.json', function (svg) {
return svg
})
stations.position_x = +stations.position_x
stations.position_y = +stations.position_y
stations.animation_time = +stations.animation_time
stations.text_x = +stations.text_x
stations.text_y = +stations.text_y
return stations
}).then(function (stations, svg) {
mount('metro-app', {
stations: stations,
svg_data: svg
})
})
回答1:
The d3-fetch module makes use of the Fetch API and will, therefore, return a Promise for each request issued via one of the module's convenience methods. To load multiple files at once you could use Promise.all which will return a single Promise that resolves once all Promises provided to the call have resolved.
import { csv, json } from 'd3-fetch'
Promise.all([
csv('/data/stations.csv'),
json('data/svg_data.json')
])
.then(([stations, svg]) => {
// Do your stuff. Content of both files is now available in stations and svg
});
Here, d3.csv
and d3.json
are provided to fetch content from two files. Once both requests have completed, i.e. both Promises have resolved, the content of each file is provided to the single Promise's .then() method call. At this point you are able to access the data and execute the rest of your code.
来源:https://stackoverflow.com/questions/49239474/load-multiple-files-using-the-d3-fetch-module