The collections read-only property of the HIDDevice interface returns an array of report formats

An array of report formats. Each entry contains the following:

usagePage

An integer representing the usage page component of the HID usage associated with this collection. The usage for a top level collection is used to identify the device type.

Standard HID usage values can be found in the HID Usage Tables document

usage

An integer representing the usage ID component of the HID usage associated with this collection.

type

An 8-bit value representing the collection type, which describes a different relationship between the grouped items. One of:

0x00

Physical (group of axes)

0x01

Application (mouse, keyboard)

0x02

Logical (interrelated data)

0x03

Report

0x04

Named array

0x05

Usage switch

0x06

Usage modified

0x07 to 0x7F

Reserved for future use

0x80 to 0xFF

Vendor-defined

More information on these types can be found in the Device Class Definition document.

children

An array of sub-collections which takes the same format as a top-level collection.

inputReports

An array of inputReport items which represent individual input reports described in this collection.

outputReports

An array of outputReport items which represent individual output reports described in this collection.

featureReports

An array of featureReport items which represent individual feature reports described in this collection.

The following example demonstrates how to access the various elements once the collections property has been returned. You can see more examples, and live demos in the article Connecting to uncommon HID devices.

for (const collection of device.collections) {
  // A HID collection includes usage, usage page, reports, and subcollections.
  console.log(`Usage: ${collection.usage}`);
  console.log(`Usage page: ${collection.usagePage}`);

  for (const inputReport of collection.inputReports) {
    console.log(`Input report: ${inputReport.reportId}`);
    // Loop through inputReport.items
  }

  for (const outputReport of collection.outputReports) {
    console.log(`Output report: ${outputReport.reportId}`);
    // Loop through outputReport.items
  }

  for (const featureReport of collection.featureReports) {
    console.log(`Feature report: ${featureReport.reportId}`);
    // Loop through featureReport.items
  }

  // Loop through subcollections with collection.children
}