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

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


var desiredSize = readableStreamDefaultControllerInstance.desiredSize;


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


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.


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

Browser compatibility

Update compatibility data on GitHub
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidEdge MobileFirefox for AndroidOpera for AndroidSafari on iOSSamsung Internet
Basic support
Chrome ? Edge ? Firefox ? IE ? Opera ? Safari ? WebView Android ? Chrome Android ? Edge Mobile ? Firefox Android ? Opera Android ? Safari iOS ? Samsung Internet Android ?


Compatibility unknown  
Compatibility unknown
Experimental. Expect behavior to change in the future.
Experimental. Expect behavior to change in the future.

Document Tags and Contributors

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