JavaScript Closures

by anandhinava

JavaScript

// once upon a time, there was a princess
var Princess = function() {

    // who rode around her world on a unicorn, battled dragons, encountered talking animals, and many other fantastical things.
    var unicorn = {
        name: 'Sparkles'
    };
    var dragons = [
        'A green one with purple wings',
        'A mean black one who breathed fire',
        'A fluffy white one that looked like a dog'
    ];
       
    var talkingAnimals = {
        squirrel: "Hello!"   
    };
    
    // and lived in a wonderful world full of adventures
    var adventures = [
        'My unicorn ' + unicorn.name + ' had a baby!',
        'I fought ' + dragons.length + ' dragons!',
        'I met a talking squirrel who said "' + talkingAnimals.squirrel + '"'
    ];
    
    var adventures1 = [
        'I fought ' + dragons.pop() + ' dragons!',
        'I fought ' + dragons.pop() + ' dragons!',
        'I fought ' + dragons.pop() + ' dragons!'
    ];

    // but she would always have to return back to her dull world of chores and grown-ups
    return {
        // and she would often tell them of her latest amazing adventure as a princess
        story: function() {
            return adventures.pop();
        },
        story1 : function() {
            return adventures1.pop();
        }
    };
};

// but all they could see is a little girl
var littleGirl = new Princess();
window.console.log(littleGirl);

// telling stories about magic and fantasy
window.console.log(littleGirl.story());
window.console.log(littleGirl.story());
window.console.log(littleGirl.story());

// a more technical example: IIFE -- Immediately invoked function execution
var db = (function() {
    // "private"
    var data = {foo:1};
    // getter/setter
    return function(key, val) {
        window.console.log('typeof data is Array: ', typeof data === 'object');
        return val === undefined ? data[key] : data[key] = val;
    };
})();

window.console.log("db('foo'): ",...