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This is an experimental technology
Check the Browser compatibility table carefully before using this in production.

The CountQueuingStrategy() constructor creates and returns a CountQueuingStrategy() object instance.


var countQS = new CountQueuingStrategy({highWaterMark});


An object containing a highWaterMark property. This is a non-negative integer defining the total number of chunks that can be contained in the internal queue before backpressure is applied.

Return value

An instance of the CountQueuingStrategy object.




const queuingStrategy = new CountQueuingStrategy({ highWaterMark: 1 });

const writableStream = new WritableStream({
  // Implement the sink
  write(chunk) {
  close() {
  abort(err) {
    console.log("Sink error:", err);
}, queuingStrategy);

var size = queuingStrategy.size();


Specification Status Comment
The definition of 'CountQueuingStrategy()' in that specification.
Living Standard Initial definition.

Browser compatibility

FeatureChromeEdgeFirefoxInternet ExplorerOperaSafari
Basic support5916571 No46 ?
FeatureAndroid webviewChrome for AndroidEdge mobileFirefox for AndroidOpera AndroidiOS SafariSamsung Internet
Basic support59591657146 ?7.0

1. From version 57: this feature is behind the dom.streams.enabled preference (needs to be set to true) and the javascript.options.streams preference (needs to be set to true). To change preferences in Firefox, visit about:config.

Document Tags and Contributors

Contributors to this page: fscholz, chrisdavidmills
Last updated by: fscholz,