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Loading data API

This module provides different methods to load data into Discovery.js applications. The public API includes the following functions:

  • loadDataFromStream(stream, options)
  • loadDataFromEvent(event, options)
  • loadDataFromFile(file, options)
  • loadDataFromUrl(url, options)
  • loadDataFromPush(options)

Each function accepts an options parameter, which is an object containing various settings that affect the behavior of the loader.

Common options

The following options are available for all the loadDataFrom* functions:

  • size (Number): An optional number representing the total size of the data being loaded (in bytes). If provided, the progress reported by the loader will be more accurate.
  • resource (Object): An optional object containing meta information about the loading resource, such as its name and creation timestamp. See the resource structure section for details.

Additional options for specific functions

loadDataFromUrl(url, options)

In addition to the Common options, the loadDataFromUrl function accepts the following additional options:

  • isResponseOk (Function): An optional function that takes a response object as an argument and returns a boolean value indicating whether the response is considered successful. Defaults to (response) => response.ok.
  • getContentSize (Function): An optional function that takes a response object as an argument and returns the size of the content being loaded. Defaults to a function that returns the value of the x-file-size header if present, or the content-length header if the URL is of the same origin and there is no content-encoding header.
  • getContentCreatedAt (Function): An optional function that takes a response object as an argument and returns the created at timestamp of the content being loaded. Defaults to a function that returns the value of the x-file-created-at header if present, or the last-modified header otherwise.
  • fetch (Object): An optional object containing additional options for the fetch function, such as method, headers, mode, etc.

resource structure

The resource object can contain the following properties (all are optional):

  • type (string): Any string
  • name (string): Any string
  • encoding (string): json or jsonxl/snapshot9, set by a loader depending on encoding
  • size (number): A size of the resource in bytes or UTF8 chars
  • encodedSize (number): An encoded size of the resource in case encoding is used (gzip or similar), i.e. the size before decoding or transfered size
  • createdAt (Date | string | number): An optional timestamp indicating when the data was created. Can be a Date object, a string in a format parseable by the Date.parse() method, or a number representing the number of milliseconds since the Unix epoch (January 1, 1970, 00:00:00 UTC).

Example:

{
  type: 'url',
  name: 'http://example.com/data.json'
  encoding: 'json',
  createdAt: '2023-04-01T12:00:00Z',
}