[Rise]

Структура conf.json такая ожидается:

[{ 
    "channel": 11,
    "message": 12,
    "reactions": [
        { "emoji": 131 },
        { "emoji": 132 }
    ]
},{ 
    "channel": 21,
    "message": 22,
    "reactions": [
        { "emoji": 231 },
        { "emoji": 232 }
    ]
}]

Тогда ошибки не будет:

var config = [{ 
    "channel": 11,
    "message": 12,
    "reactions": [
        { "emoji": 131 },
        { "emoji": 132 }
    ]
},{ 
    "channel": 21,
    "message": 22,
    "reactions": [
        { "emoji": 231 },
        { "emoji": 232 }
    ]
}];
for (var { channel, message: message_id, reactions } of config) {
    console.log('for#1', channel, message_id, reactions);
    for (var { emoji } of reactions) {
        console.log('for#2', emoji);
    }
}