Imports and Exports

Code

// Imports provided to a WASM module
const importObject = {
  env: {
    consoleLog: (value) => console.log("from wasm:", value),
    now: () => Date.now(),
    memory: new WebAssembly.Memory({ initial: 1 }),
  },
};

const { instance } = await WebAssembly.instantiate(bytes, importObject);

// Exports can be functions, memory, tables, or globals
const { add, multiply, memory, __heap_base } = instance.exports;

console.log(add(2, 3));        // 5
console.log(multiply(4, 5));   // 20
console.log("heap starts at", __heap_base);

Explanation

Imports are host-provided functions, memory, tables, or globals grouped under module names that the WASM module references. Exports are the module's public surface, exposed as properties of instance.exports. This two-way bridge is how WASM calls into JS and how JS invokes compiled functions.

More WebAssembly Snippets