Import and Export

WebAssembly modules communicate through a well-defined import/export system. This enables powerful inter-module communication.

Export System

Exports make functions, memory, and tables available to the outside world.

Export Functions

(module
  (func (export "greet") (result i32)
    (i32.const 42)))

;; JavaScript usage:
const result = instance.exports.greet(); // 42

Export Memory

(module
  (memory (export "memory") 1))

;; JavaScript usage:
const memory = instance.exports.memory;
const view = new Uint8Array(memory.buffer);
view[0] = 100;

Import System

Imports let WASM use functions and memory provided by the host environment.

Basic Import

(module
  (import "env" "log" (func $log (param i32)))
  (func (export "process") (param i32 i32)
    local.get 0
    local.get 1
    i32.add
    call $log))

const importObject = {
  env: {
    log: (value) => console.log('WASM says:', value)
  }
};

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

Best Practices

1. Organize by namespace — Group imports by namespace (console, env, js)
2. Type safety — Exactly match WASM types with import signatures
3. Error handling — Use error codes or exceptions
4. Minimize imports — Each import has overhead

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Continue learning Type System for detailed type information.