Calling JS from Zig

[luisjakon]

Hello, not sure if it is somewhere in the docs...but is it possible to make calls into the JS host environment in a generic way?

// something along these lines... (inspired by the zig-js package)
const js = @import("zigar-js");

pub fn say_hello() !void {
    try js.global("console").call("log", .{js.string("Hello from Zig!")}, void);
}

If not, what would be the best way to do this?

I also couldn't figure out how to introduce these definitions into the runtime environment:

// This function should be provided by the JS host
extern fn console_log(value: *[]u8);

pub fn say_hello() void {
  console_log("Hello from Zig!");
}

I can see the entry is the generated by looking at the resulting wasm file, but not sure how to pass it as an import function/object prior to the WebAssembly instance initialization.

Any help, clarifications or direction would be greatly appreciated.

Many thanks!

[chung-leong]

Currently, no. You have to call a function pointer of a specific type. Generally, we want to avoid referencing JavaScript values in Zig since we have no garbage collection there. A theoretical implement of your example would lock both console and "Hello from Zig!" into memory forever, since it's impossible to determine if these JavaScript values are still being referenced.

What we do perhaps is to have a Zig function that emits an anytype message to the JavaScript side. Something like this:

const zigar = @import("zig");

pub fn say_hello() !void {
    try zigar.js.emit(.log, .{ .message = "Hello from Zig!" });
}

import { __zigar, say_hello } from 'zig/test.zig';

__zigar.on('event', (type, arg) => {
    switch (type) {
        case 'log':
            console.log(arg.message.string);
            break;
    }
});

say_hello();

Of course, we're using console here only as an example. You'd use std.debug.print() normally.