GPUBuffer: mapAsync() method

{{APIRef("WebGPU API")}}{{SecureContext_Header}}{{AvailableInWorkers}}

The mapAsync() method of the {{domxref("GPUBuffer")}} interface maps the specified range of the GPUBuffer. It returns a {{jsxref("Promise")}} that resolves when the GPUBuffer's content is ready to be accessed. While the GPUBuffer is mapped it cannot be used in any GPU commands.

Once the buffer is successfully mapped (which can be checked via {{domxref("GPUBuffer.mapState")}}), calls to {{domxref("GPUBuffer.getMappedRange()")}} will return an {{jsxref("ArrayBuffer")}} containing the GPUBuffer's current values, to be read and updated by JavaScript as required.

When you have finished working with the GPUBuffer values, call {{domxref("GPUBuffer.unmap()")}} to unmap it, making it accessible to the GPU again.

Syntax

mapAsync(mode)
mapAsync(mode, offset, size)

Parameters

• mode

  • : A {{glossary("bitwise flags", "bitwise flag")}} that specifies whether the GPUBuffer is mapped for reading or writing. Possible values are:

    • GPUMapMode.READ

      • : The GPUBuffer is mapped for reading. Values can be read, but any changes made to the {{jsxref("ArrayBuffer")}} returned by {{domxref("GPUBuffer.getMappedRange()")}} will be discarded once {{domxref("GPUBuffer.unmap()")}} is called.

        Read-mode mapping can only be used on GPUBuffers that have a usage of GPUBufferUsage.MAP_READ set on them (i.e., when created with {{domxref("GPUDevice.createBuffer()")}}).

    • GPUMapMode.WRITE

      • : The GPUBuffer is mapped for writing. Values can be read and updated — any changes made to the {{jsxref("ArrayBuffer")}} returned by {{domxref("GPUBuffer.getMappedRange()")}} will be saved to the GPUBuffer once {{domxref("GPUBuffer.unmap()")}} is called.

        Write-mode mapping can only be used on GPUBuffers that have a usage of GPUBufferUsage.MAP_WRITE set on them (i.e., when created with {{domxref("GPUDevice.createBuffer()")}}).

• offset {{optional_inline}}

  • : A number representing the offset, in bytes, from the start of the buffer to the start of the range to be mapped. If offset is omitted, it defaults to 0.

• size {{optional_inline}}

  • : A number representing the size, in bytes, of the range to be mapped. If size is omitted, the range mapped extends to the end of the GPUBuffer.

Return value

A {{jsxref("Promise")}} that resolves to {{jsxref("Undefined")}} when the GPUBuffer's content is ready to be accessed.

Validation

The following criteria must be met when calling mapAsync(), otherwise an OperationError {{domxref("DOMException")}} is thrown, the promise is rejected, and a {{domxref("GPUValidationError")}} is generated:

• offset is a multiple of 8.
• The total range to be mapped (size if specified, or {{domxref("GPUBuffer.size")}} - offset if not) is a multiple of 4.
• The total range to be mapped is inside the bounds of the GPUBuffer.
• If mode is GPUMapMode.READ, the GPUBuffer has a usage of GPUBufferUsage.MAP_READ.
• If mode is GPUMapMode.WRITE, the GPUBuffer has a usage of GPUBufferUsage.MAP_WRITE.

Examples

See the main GPUBuffer page for an example.

Specifications

{{Specifications}}

Browser compatibility

{{Compat}}

See also

• The WebGPU API