// Functions as values
const greet = function(name) {
    return 'Hello, ' + name;
};

// Functions as arguments
function map(array, transform) {
    const result = [];
    for (let i = 0; i < array.length; i++) {
        result.push(transform(array[i]));
    }
    return result;
}

const doubled = map([1, 2, 3], function(x) { return x * 2; });

// Functions returning functions
function multiplier(factor) {
    return function(number) {
        return number * factor;
    };
}

const double = multiplier(2);
const triple = multiplier(3);
double(5);  // 10
triple(5);  // 15

// Closures capture their lexical environment
function createCounter() {
    let count = 0;  // Private state
    
    return {
        increment: function() { return ++count; },
        decrement: function() { return --count; },
        value: function() { return count; }
    };
}

const counter = createCounter();
counter.increment();  // 1
counter.increment();  // 2
counter.value();      // 2
// count is not directly accessible

// Objects inherit from objects
const animal = {
    speak: function() {
        return this.sound;
    }
};

const dog = Object.create(animal);
dog.sound = 'Woof!';
dog.speak();  // 'Woof!'

const cat = Object.create(animal);
cat.sound = 'Meow!';
cat.speak();  // 'Meow!'

// The prototype chain
dog.hasOwnProperty('sound');  // true
dog.hasOwnProperty('speak');  // false (inherited)

// Objects are dynamic property bags
const obj = {};

// Add properties anytime
obj.name = 'Dynamic';
obj['computed-key'] = 'Works too';

// Delete properties
delete obj.name;

// Check existence
'computed-key' in obj;  // true

// Iterate properties
for (const key in obj) {
    if (obj.hasOwnProperty(key)) {
        console.log(key, obj[key]);
    }
}