Dynamic Memory Allocation with malloc

<!doctype html>
  <script>
    function fetchAndCompileWasmModules (urls) {
      return Promise.all(urls.map(url => {
        return fetch(url)
        .then(res => {
          if (res.ok)
            return res.arrayBuffer();
          throw new Error(`Unable to fetch Web Assembly file ${url}.`);
        })
        .then(bytes => WebAssembly.compile(bytes));
      }));
    }

    let wasmMalloc, wasmFree;
    fetchAndCompileWasmModules([
      'https://cdn.rawgit.com/guybedford/wasm-intro/a1e23253/6-dynamic-wasm-memory-malloc/program.wasm',
      'https://cdn.rawgit.com/guybedford/wasm-intro/a1e23253/6-dynamic-wasm-memory-malloc/memory.wasm'
    ])
    .then(([program, memory]) => {
      return WebAssembly.instantiate(program, {
        env: {
          malloc: len => wasmMalloc(len),
          free: addr => wasmFree(addr)
        }
      })
      .then(m => {
        return WebAssembly.instantiate(memory, {
          env: {
            memory: m.exports.memory
          }
        })
        .then(m => {
          wasmMalloc = m.exports.malloc;
          wasmFree = m.exports.free;
        })
        .then(() => {
          console.log(m.exports.createRecord(2, 1.1, 2.2));
        });
      });
    });
  </script>

#include <stdlib.h>

struct Record {
  int id;
  float x;
  float y;
};

struct Record* createRecord (int id, float x, float y) {
  struct Record* record = malloc(sizeof(struct Record));
  record->id = id;
  record->x = x;
  record->y = y;
  return record;
}

void deleteRecord (struct Record* record) {
  free(record);
}