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

The size() method of the ByteLengthQueueingStrategy interface returns the given chunk’s byteLength property.


var size = byteLengthQueuingStrategyInstance.size(chunk);


A chunk of data being passed through the stream.

Return value

An integer representing the byte length of the given chunk.


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

const readableStream = new ReadableStream({
  start(controller) {
  pull(controller) {
  cancel(err) {
    console.log("stream error:", err);
}, queuingStrategy);

var size = queueingStrategy.size(chunk);


Specification Status Comment
The definition of 'size' 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, ricea
Last updated by: fscholz,