Foreign Function Interface

Foreign Function Interface (FFI) is a way to call functions written in other languages from JavaScript.

Prerequisites: - Julia from https://julialang.org/downloads/ installed - `julia` in your `PATH`

This example shows how to use the julia FFI library to execute Julia code from Deno.

First lets define the symbols we want to import from the library.

const SYMBOLS = {

The `jl_init` function initializes the Julia runtime.

  jl_init: {

The function takes no parameters so we pass an empty array.

    parameters: [],

The function returns a `void` pointer.

    result: "void",
  },

The `jl_eval_string` function takes a string and evaluates it as Julia code.

  jl_eval_string: {

The function takes a string so we pass an array with a buffer type

    parameters: ["buffer"],

The function results in a `pointer`.

    result: "pointer",
  },
} as const;

Next, we import the FFI library from Deno.

const julia = Deno.dlopen(

Change .dll to .dylib on macOS and .so on Linux

  `libjulia.dll`,
  SYMBOLS,
).symbols;

Before we can call the functions we need to convert the string to a C string. Let's define a helper function for that.

export function cstr(str: string): Uint8Array {
  const buf = new Uint8Array(str.length + 1);
  new TextEncoder().encodeInto(str, buf);
  return buf;
}

We can now call the functions we imported.

julia.jl_init();

We can now evaluate Julia code.

julia.jl_eval_string(
  cstr("println(sqrt(2.0))"),
);

Run this example locally using the Deno CLI:

deno run --unstable --allow-ffi https://byexample-9vp6gpfrkxbp.deno.dev/ffi.ts

Additional resources:

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