Web/API/ReadableStreamDefaultController/desiredSize

The desiredSize read-only property of the ReadableStreamDefaultController interface returns the desired size required to fill the stream's internal queue.

Syntax

var desiredSize = readableStreamDefaultController.desiredSize;

Value

An integer. Note that this can be negative if the queue is over-full.

Examples

The A readable stream with an underlying push source and backpressure support example in the spec provides a good example of using desiredSize to manually detect when the stream is full and apply backpressure, and also of using ReadablestreamDefaultController.error() to manually trigger a stream error if another part of the system it relies on fails.

Specifications

Specification	Status	Comment
StreamsThe definition of 'desiredSize' in that specification.	Living Standard	Initial definition.

Browser compatibility

The compatibility table in this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request.

Update compatibility data on GitHub

	Desktop						Mobile
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet
desiredSize Experimental'	Chrome ?	Edge ?	Firefox Full support 65 Full support 65 Full support 57 Disabled' Disabled' 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.	IE No support No	Opera ?	Safari ?	WebView Android ?	Chrome Android ?	Firefox Android Full support 65 Full support 65 Full support 57 Disabled' Disabled' 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.	Opera Android ?	Safari iOS ?	Samsung Internet Android ?

Legend

Full support  

Full support

No support  

No support

Compatibility unknown  

Compatibility unknown

Experimental. Expect behavior to change in the future.'

Experimental. Expect behavior to change in the future.

User must explicitly enable this feature.'

User must explicitly enable this feature.

ReadableStreamDefaultController.desiredSize by Mozilla Contributors is licensed under CC-BY-SA 2.5.