Variables - chung-leong/zigar GitHub Wiki

Variables declared in a Zig module are accessible in JavaScript provided they're public. Unlike constants, variables cannot be imported individually. You must access them through the module, represented by the default export:

const std = @import("std");

pub const numeric_constant: i32 = 1234;
pub var numeric_variable: i32 = 43;

pub fn printNumericVariable() {
    std.debug.print("From Zig: {d}\n", .{numeric_variable});
}

import module, { numeric_constant, printNumericVariable } from './variable-example-1.zig';

console.log(numeric_constant);
console.log(module.numeric_variable);
module.numeric_variable = 777;
printNumericVariable();

1234
43
From Zig: 777

Limitations

A pointer that exist in the Zig memory space can only point to objects living in the same space. It cannot point to an object in JavaScript memory, where objects be garbage-collected at any time. An error would occur if you attempt to assign such an object to a pointer variable in a module:

const std = @import("std");

pub const User = struct {
    name: []const u8,
    role: []const u8,
};

pub const default_user: User = .{
    .name = "nobody",
    .role = "none",
};
pub var current_user: *const User = &default_user;

pub fn printCurrentUser() void {
    std.debug.print("{s} ({s})\n", .{ current_user.name, current_user.role });
}

import module, { printCurrentUser, User } from './variable-example-2.zig';

printCurrentUser();
try {
    module.current_user = new User({ name: 'batman72', role: 'vigilante' });
} catch (err) {
    console.log(err.message);
}

nobody (none)
Pointers in Zig memory cannot point to garbage-collected object

In order to create an object that exists in Zig's memory space, you'd need to get an Allocator from Zig and supply it to the constructor using its optional options argument:

const std = @import("std");

pub const User = struct {
    name: []const u8,
    role: []const u8,
};

pub const default_user: User = .{
    .name = "nobody",
    .role = "none",
};
pub var current_user: *const User = &default_user;
var gpa = std.heap.DebugAllocator(.{}).init;
pub const allocator = gpa.allocator();

pub fn printCurrentUser() void {
    std.debug.print("{s} ({s})\n", .{ current_user.name, current_user.role });
}

import module, { allocator, printCurrentUser, User } from './variable-example-3.zig';

printCurrentUser();
module.current_user = new User({ name: 'batman72', role: 'vigilante' }, { allocator });
printCurrentUser();

nobody (none)
batman72 (vigilante)