Quickstart

The WebNN (Web Neural Network) API enables neural network operations in web applications by implementing computational graphs. A computational graph is a directed graph where nodes represent operations or input variables, with each node’s output serving as input for subsequent nodes.

Working with Operations and Tensors

The API uses two primary abstractions:

Operand objects represent tensors (multi-dimensional arrays) that can be inputs, outputs, or constants
MLContext provides operations for building and executing computational graphs

Graph Lifecycle

The WebNN API supports four main phases:

Building the computational graph
Compiling the graph
Executing the graph
Integrating with other Web APIs for input data (e.g., media APIs for images/video frames or sensor APIs for sensory data)

Here’s a basic example that demonstrates building, compiling, and executing a graph with operations, inputs, and output. For comprehensive model construction patterns, refer to the detailed tutorials.

Build Your First Graph with WebNN API

C = 0.2 \cdot A + B

executing-an-MLGraph-using-MLTensors.js


const descriptor = {dataType: 'float32', shape: [2, 2]};
const context = await navigator.ml.createContext();
const builder = new MLGraphBuilder(context);
 
// 1. Create a computational graph 'C = 0.2 * A + B'.
const constant = builder.constant(descriptor, new Float32Array(4).fill(0.2));
const A = builder.input('A', descriptor);
const B = builder.input('B', descriptor);
const C = builder.add(builder.mul(A, constant), B);
 
// 2. Compile the graph.
const graph = await builder.build({'C': C});
 
// 3. Create reusable input and output tensors.
const [inputTensorA, inputTensorB, outputTensorC] =
    await Promise.all([
      context.createTensor({
        dataType: A.dataType, shape: A.shape, writable: true
      }),
      context.createTensor({
        dataType: B.dataType, shape: B.shape, writable: true
      }),
      context.createTensor({
        dataType: C.dataType, shape: C.shape, readable: true
      })
    ]);
 
// 4. Initialize the inputs.
context.writeTensor(inputTensorA, new Float32Array(4).fill(1.0));
context.writeTensor(inputTensorB, new Float32Array(4).fill(0.8));
 
// 5. Execute the graph.
const inputs = {
  'A': inputTensorA,
  'B': inputTensorB
};
const outputs = {
  'C': outputTensorC
};
context.dispatch(graph, inputs, outputs);
    
// 6. Read back the computed result.
const result = await context.readTensor(outputTensorC);
console.log('Output value:', new Float32Array(result));  // [1, 1, 1, 1]