Instrumentation for Javascript Applications
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Latest commit 7feeb89 Sep 11, 2018


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A blazingly fast performance stat monitoring and collection library for node or the browser.


npm install heimdalljs

How fast?

Heimdall allows for 2 forms of stat collection: counter based and time based.

The overhead of time based stat collection is the cost of allocating a tiny TypedArray, a four element Array, and On Desktop Chrome on a 2015 era MacBook Pro this amounts to roughly 200 nanoseconds. You can easily run the benchmarks on devices you care about to see what the cost will be for you.

The overhead of counter based collection is the cost of a method call with two bitwise operations and an integer increment. An occasional Uint32Array allocation is thrown in when more space is needed. The cost here is pragmatically negligible, and counters are ideal for situations in which the overhead of a timer is enough to significantly alter stats.



const heimdall = new Heimdall();


start timing something

const token = heimdall.start('<label>');

stop timing something



A monitor is a group of counters which you can increment as needed to track things such as entry into a function or object creations.


let condition = heimdall.hasMonitor('<name>');


When you register a monitor, the first argument functions as the unique name for that monitor, while all other arguments (labels) will be the name of a specific counter in your group of counters.

The call to registerMonitor will give you back an object with your labels as its keys and the token to increment as the value at that key.

const tokens = heimdall.registerMonitor('<name>', ...labels);

Full Example:

const { foo, bar, baz } = heimdall.registerMonitor('my-first-monitor', 'foo', 'bar', 'baz');

heimdall.increment(foo); // increment 'foo' counter in the 'my-first-monitor' group.




configFor toJSON

For the documentation for HeimdallTree see .

Removing Heimdall from production builds.

If desired, heimdall can be stripped from production builds using this plugin for Babel5 or this plugin for Babel6.

Global Session

Heimdall tracks a graph of timing and domain-specific stats for performance. Stat collection and monitoring is separated from graph construction to provide control over context detail. Users can create fewer nodes to have reduced performance overhead, or create more nodes to provide more detail.

Since the graph needs to be global, node may have multiple different versions of heimdalljs loaded at once. Each one will have its own Heimdall instance, but will use the same session, saved on process. This means that the session will have a heterogeneous graph of HeimdallNodes. For this reason, versions of heimdalljs that change Session, or the APIs of HeimdallNode or Cookie will use a different property to store their session (process._heimdall_session_<n>). Please note, this can result in lost detail & lost stats. To mitigate this issue, the recomendation would be to detect this situation and issue a warning.


If you are using Visual Studio Code for development, you might want to install both typescript and tslint packages via yarn.

yarn global add typescript tslint