The read-only offset property of the ConstantSourceNode interface returns a AudioParam object indicating the numeric a-rate value which is always returned by the source when asked for the next sample.

While the AudioParam named offset is read-only, the value property within is not. So you can change the value of offset by setting the value of ConstantSourceNode.offset.value:

myConstantSourceNode.offset.value = newValue;


let offsetParameter = ConstantAudioNode.offset;

let offset = ConstantSourceNode.offset.value;
ConstantSourceNode.offset.value = newValue;


An AudioParam object indicating the a-rate value returned for every sample by this node. The default value is 1.0.

To access the offset parameter's current value, access the parameter's value property, as shown in the syntax box above.


This example shows how to set up a ConstantSourceNode so its offset is used as the input to a pair of GainNodes; this snippet is derived from the complete example you can find in Controlling multiple parameters with ConstantSourcenode.

gainNode2 = context.createGain();
gainNode3 = context.createGain();
gainNode2.gain.value = gainNode3.gain.value = 0.5;

volumeSliderControl.value = gainNode2.gain.value;

constantNode = context.createConstantSource();

First, the gain nodes are created and configured, and a slider control's value is set to match the gain on the two nodes. Then we create a new ConstantSourceNode and make it the source for the two gain nodes' GainNode.gain values. Each of those values is also an AudioParam.

Let's say we have an event handler (for click events, in this case) which needs to respond by altering the value of the two gain nodes. With the linkage above in place, that can be done using this simple event handler:

function handleClickEvent(event) {
  volumeSliderControl.value = constantSource.offset.value;

All this function has to do is fetch the current value of the slider control we're using to control the paired nodes' gains, then store that value into the ConstantSourceNode's offset parameter. That's done by simply changing the contents of its AudioParam.value property. The two gain nodes quickly adopt the new volume level.


Specification Status Comment
Web Audio API
The definition of 'offset' in that specification.
Working Draft

Browser compatibilityUpdate compatibility data on GitHub

Chrome Edge Firefox Internet Explorer Opera Safari
Basic support 56 No 52 — 53
52 — 53
This property is still available, but via the inheritance of AudioScheduledSourceNode.
No No No
Android webview Chrome for Android Edge Mobile Firefox for Android Opera for Android iOS Safari Samsung Internet
Basic support No No No 52 — 53
52 — 53
This property is still available, but via the inheritance of AudioScheduledSourceNode.
No No No

See also

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