gistfile1.txt

var before = {
    "12": "John",
    "100": "Mary"
};

var after = [],
    k;

for (k in before) {
    if (before.hasOwnProperty(k)) {
        after.push({ value: k, label: before[k] });
    }
}

// after is now
[
    { value: "12", label: "John" },
    { value: "100", label: "Mary" }
]