var object = {
    "N102 - Number 102": {name: "1N02 - Number 102"},
    "N104 - Number 104": {name: "N104 - Number 104"},
    "N100 - Number 100": {name: "N100 - Number 100"},
    "N155 - Number 155": {name: "N155 - Number 155"},
    "N126 - Number 126": {name: "N126 - Number 126"},
    "N152 - Number 152": {name: "N152 - Number 152"},
    "N110 - Number 110": {name: "N110 - Number 110"},
    "N156 - Number 156": {name: "N156 - Number 156"}
};

var min, max;
for (key in object) {
    var value = parseInt(key.match(/d+/)[0]);
    !min ? min = value : value < min ? min = value : true;
    !max ? max = value : value > max ? max = value : true;
}