Performance: measureUserAgentSpecificMemory() method

The browser automatically allocates memory when objects are created and frees it when they are not reachable anymore (garbage collection). This garbage collection (GC) is an approximation since the general problem of determining whether or not a specific piece of memory is still needed is impossible (see also JavaScript Memory Management). Developers need to make sure that objects are garbage collected, memory isn't leaked, and memory usage doesn't grow unnecessarily over time leading to slow and unresponsive web applications. Memory leaks are typically introduced by forgetting to unregister an event listener, not closing a worker, accumulating objects in arrays, and more.

The measureUserAgentSpecificMemory() API aggregates memory usage data to help you find memory leaks. It can be used for memory regression detection or for A/B testing features to evaluate their memory impact. Rather than make single calls to this method, it's better to make periodic calls to track how memory usage changes over the duration of a session.

The byte values this API returns aren't comparable across browsers or between different versions of the same browser as these are highly implementation dependent. Also, how breakdown and attribution arrays are provided is up to the browser as well. It is best to not hardcode any assumptions about this data. This API is rather meant to be called periodically (with a randomized interval) to aggregate data and analyze the difference between the samples.

None.

A Promise that resolves to an object containing the following properties:

bytes

A number representing the total memory usage.

breakdown

An Array of objects partitioning the total bytes and providing attribution and type information. The object contains the following properties:

bytes

The size of the memory that this entry describes.

attribution

An Array of container elements of the JavaScript realms that use the memory. This object has the following properties:

url

If this attribution corresponds to a same-origin JavaScript realm, then this property contains the realm's URL. Otherwise it is the string "cross-origin-url".

container

An object describing the DOM element that contains this JavaScript realm. This object has the following properties:

id

The id attribute of the container element.

src

The src attribute of the container element. If the container element is an <object> element, then this field contains the value of the data attribute.

scope

A string describing the type of the same-origin JavaScript realm. Either "Window", "DedicatedWorkerGlobalScope", "SharedWorkerGlobalScope", "ServiceWorkerGlobalScope" or "cross-origin-aggregated" for the cross-origin case.

types

An array of implementation-defined memory types associated with the memory.

An example return value looks like this:

{
  bytes: 1500000,
  breakdown: [
    {
      bytes: 1000000,
      attribution: [
        {
          url: "https://example.com",
          scope: "Window",
        },
      ],
      types: ["DOM", "JS"],
    },
    {
      bytes: 0,
      attribution: [],
      types: [],
    },
    {
      bytes: 500000,
      attribution: [
        {
          url: "https://example.com/iframe.html"
          container: {
            id: "example-id",
            src: "redirect.html?target=iframe.html",
          },
          scope: "Window",
        }
      ],
      types: ["JS", "DOM"],
    },
  ],
}

SecurityError DOMException

Thrown if the security requirements for preventing cross-origin information leaks aren't fulfilled.

Your site needs to be in a secure context.

Two headers need to be set to cross-origin isolate your site:

• Cross-Origin-Opener-Policy with same-origin as value (protects your origin from attackers)
• Cross-Origin-Embedder-Policy with require-corp or credentialless as value (protects victims from your origin)

Cross-Origin-Opener-Policy: same-origin
Cross-Origin-Embedder-Policy: require-corp

To check if cross origin isolation has been successful, you can test against the crossOriginIsolated property available to window and worker contexts:

if (crossOriginIsolated) {
  // Use measureUserAgentSpecificMemory
}

The following code shows how to call the measureUserAgentSpecificMemory() method once every five minutes at a random interval using Exponential distribution.

function runMemoryMeasurements() {
  const interval = -Math.log(Math.random()) * 5 * 60 * 1000;
  console.log(`Next measurement in ${Math.round(interval / 1000)} seconds.`);
  setTimeout(measureMemory, interval);
}

async function measureMemory() {
  const memorySample = await performance.measureUserAgentSpecificMemory();
  console.log(memorySample);
  runMemoryMeasurements();
}

if (crossOriginIsolated) {
  runMemoryMeasurements();
}

• setTimeout
• Monitor your web page's total memory usage with measureUserAgentSpecificMemory() - web.dev