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function deepFreeze(obj) {
    // Retrieve the property names defined on obj
    var propNames = Object.getOwnPropertyNames(obj);

    // Freeze properties before freezing self
    propNames.forEach(function(name) {
        var prop = obj[name];

        // Freeze prop if it is an object
        if (typeof prop == 'object' && prop !== null) {        
            deepFreeze(prop);
        }
    });

    // Freeze self (no-op if already frozen)
    return Object.freeze(obj);
}