Error Handling

A failing GTKX binding throws a JavaScript exception, so you handle it with try/catch, exactly as you would around any other JavaScript code. No GError** out-parameter ever appears in a JS signature.

Promisified methods reject with the same errors, so try { await ... } catch handles synchronous and asynchronous failures identically. See Async Operations for the promise model and cancellation.

GErrors come only from GI bindings. Everything else in a GTKX app throws ordinary JavaScript errors, and both land on the same try/catch channel.

What you catch: GLib.Error

A thrown GError is an instance of GLib.Error from @gtkx/gi/glib, and that class extends the built-in Error. On top of the standard Error surface it exposes three fields:

• message: the human-readable description GLib produced.
• domain: the error domain, a number.
• code: the domain-specific error code, a number.

Matching errors by domain and code

Each error domain is generated as an object that works as the right-hand side of instanceof. The check matches the domain only, so pair it with a code comparison against the same object's members:

import * as GLib from "@gtkx/gi/glib";

const contents = "not a key file";
const keyFile = GLib.KeyFile.new();

try {
    keyFile.loadFromData(contents, Buffer.byteLength(contents), GLib.KeyFileFlags.NONE);
} catch (error) {
    if (error instanceof GLib.KeyFileError && error.code === GLib.KeyFileError.PARSE) {
        // not a valid key file
    } else {
        throw error;
    }
}

Domain objects exist in every namespace whose library registers them, such as GLib.KeyFileError, Gio.IOErrorEnum, and Gtk.DialogError.

A successful instanceof check against a domain object narrows the value to { domain, code, message }, not to GLib.Error. Reaching methods like matches or copy requires testing error instanceof GLib.Error.

To build a GError of your own rather than catch one, see GLib.Error.newLiteral in OpenGL.

Next

Continue with Components for how GTKX widgets compose and the hooks that drive them.