rookie question - let, scope, and callbacks

[Amy C <mathematical coffee gmail com>]

Hi all,

I've made myself a whole bunch of PopupSwitchMenuItems and tried to
connect their 'toggled' callback to the same function, passing the
name of the menu item as a parameter:

    this._items = {};
    this._toggleNames = {
                         ignorePopups   : _('Ignore popups'),
                         ignoreMaximised: _('Ignore maximised windows'),
                         DEBUG: _('Debug mode')
    };
    for ( let propName in this._toggleNames ) {
            this._items[propName] = new
PopupMenu.PopupSwitchMenuItem(this._toggles[propName], false);
            this._items[propName].connect('toggled', Lang.bind(this,
function() { log(('toggled: ' + propName)); }));
            // ... rest of code
    }

However when I toggle any of the items, I always get "toggled: DEBUG"
as the output (this also occurs when I remove the Lang.bind, although
I will eventually need it).

Why is this happening? propName is only declared in the for statement,
and I thought the use of 'let' made sure that `propName` didn't
default to the last value that it had for the callbacks, i.e. DEBUG.

I'm using GNOME 3.4.

cheers!