The Network Information API provides information about the system's connection in terms of general connection type (e.g., 'wifi, 'cellular', etc.). This can be used to select high definition content or low definition content based on the user's connection.

The interface consists of a single NetworkInformation object, an instance of which is returned by the Navigator.connection property.

NetworkInformation

Provides information about the connection a device is using to communicate with the network and provides a means for scripts to be notified if the connection type changes. The NetworkInformation interface cannot be instantiated. It is instead accessed through the Navigator interface.

This example watches for changes to the user's connection.

let type = navigator.connection.effectiveType;

function updateConnectionStatus() {
  console.log(
    `Connection type changed from ${type} to ${navigator.connection.effectiveType}`,
  );
  type = navigator.connection.effectiveType;
}

navigator.connection.addEventListener("change", updateConnectionStatus);

The connection object is useful for deciding whether to preload resources that take large amounts of bandwidth or memory. This example would be called soon after page load to check for a connection type where preloading a video may not be desirable. If a cellular connection is found, then the preloadVideo flag is set to false. For simplicity and clarity, this example only tests for one connection type. A real-world use case would likely use a switch statement or some other method to check all of the possible values of NetworkInformation.type. Regardless of the type value you can get an estimate of connection speed through the NetworkInformation.effectiveType property.

let preloadVideo = true;
const connection = navigator.connection;
if (connection) {
  if (connection.effectiveType === "slow-2g") {
    preloadVideo = false;
  }
}

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