main.js

const fs = require('fs');

const mathWASM = fs.readFileSync('./math.wasm');
const mainWASM = fs.readFileSync('./main.wasm');

async function main() {
  // Both modules will share this table
  const table = new WebAssembly.Table({
    element: "anyfunc",
    initial: 3,
  })

  imports = { env: { table } }
  const mathModule = await WebAssembly.instantiate(mathWASM, imports);
  // The math module populates the table like this: 
  // | $add | $sub | $mul |

  const mainModule = await WebAssembly.instantiate(mainWASM, imports);

  // main calls the function at zero index in the table: $add
  console.log(mainModule.instance.exports.foo(7, 3)); // 10
  
  swapTableIndices(table, 0, 1);
  // now: | $sub | $add | $mul |

  console.log(mainModule.instance.exports.foo(7, 3)); // 4

  swapTableIndices(table, 0, 2);
  // now | $mul | $add | $sub |

  console.log(mainModule.instance.exports.foo(7, 3)); // 21
}

main();

// WASM is not yet able to modify the table internally
// aside from adding functions during initilization 
function swapTableIndices(table, i, j) {
  const f = table.get(i);
  const g = table.get(j);

  table.set(i, g);
  table.set(j, f);
}

main.wat

(module
  (type (;0;) (func (param i32 i32) (result i32)))
  (import "env" "table" (table (;0;) 1 funcref))
  (func (;0;) (type 0) (param i32 i32) (result i32)
    local.get 0
    local.get 1
    i32.const 0 ;; index of function in table
    call_indirect (type 0) (;type of function being called;))
  (memory (;0;) 2)
  (export "foo" (func 0)))

math.wat

(module
  (type (;0;) (func))
  (type (;1;) (func (param i32 i32) (result i32)))
  (import "env" "table" (table (;0;) 3 funcref))
  (func $add (;0;) (type 1) (param i32 i32) (result i32)
    local.get 1
    local.get 0
    i32.add)
  (func $sub (;1;) (type 1) (param i32 i32) (result i32)
    local.get 0
    local.get 1
    i32.sub)
  (func $mul (;2;) (type 1) (param i32 i32) (result i32)
    local.get 0
    local.get 1
    i32.mul)
  (memory (;0;) 2)
  (export "memory" (memory 0))
  (elem (;0;)
    (i32.const 0) ;; table offset
    $add $sub $mul;; add funcs to table
    ))