walloc

malloc() and free() bindings for WebAssembly in JavaScript.

Basic Usage

Pass an absolute filename to the walloc() function. The result is the exports property of a WebAssembly.Instance.

'use strict';
const Walloc = require('walloc');
const memory = new WebAssembly.Memory({ initial: 256, maximum: 256 });
const walloc = new Walloc({
  memory,
  getTotalMemory () { return memory.buffer.byteLength; }
});

const ptr = walloc.malloc(2048);  // Allocate 2048 bytes.
// Do something with the allocated memory.
walloc.free(ptr); // Free the memory.

API

walloc exports a single class with the following API.

Walloc(options) constructor

• Arguments
  • options (object) - A configuration object supporting the following schema.
    • DYNAMICTOP_PTR (number) - The value sbrk() returns. Optional. Defaults to 0.
    • STACKTOP (number) - The top of the stack. Optional. Defaults to 0.
    • memory (object) - An instance of WebAssembly.Memory.
    • abort(err) (function) - A function that is called when an error occurs. The error is passed as the err parameter. Optional. Defaults to a function that throws err.
    • abortOnCannotGrowMemory() (function) - A function that is called when memory allocation fails, and the WebAssembly memory cannot be grown. Optional. Defaults to a function that calls abort() with an error.
    • enlargeMemory() (function) - A function that attempts to grow the WebAssembly memory. Optional. Defaults to a function that calls abortOnCannotGrowMemory().
    • getTotalMemory() (function) - A function that returns the total size of the memory. Optional. Defaults to a function that returns 0.
    • ___setErrNo(errno) (function) - A function that sets errno in C. Optional.

Constructs a new allocator instance. Must be called with new.

Walloc.prototype.malloc(size)

• Arguments
  • size (number) - The number of bytes to allocate.
• Returns
  • ptr (number) - The base address of the allocated memory in the WebAssembly memory.

Attempts to allocate a block of memory with size size. On success, the base address is returned. Throws if memory cannot be allocated.

Walloc.prototype.free(ptr)

• Arguments
  • ptr (number) - The base address of the allocated memory block being freed.
• Returns
  • Nothing

Releases the block of memory with base address ptr.