underscorejs 一共1500行的代码，很多functional programming的思想

// underscore
var arr6 = _.map(arr1, function(item) { return item * 3 });
console.log(arr6);

var arr7 = _.filter([2,3,4,5,6,7], function(item) { return item % 2 === 0; });
console.log(arr7);

var person = {
    firstname: 'Default',
    lastname: 'Default',
    getFullName: function() {
        return this.firstname + ' ' + this.lastname;  
    }
}

var john = {
    firstname: 'John',
    lastname: 'Doe'
}

// don't do this EVER! for demo purposes only!!!
john.__proto__ = person;

for (var prop in john) {
    if (john.hasOwnProperty(prop)) {
        console.log(prop + ': ' + john[prop]);
    }
}

var jane = {
    address: '111 Main St.',
    getFormalFullName: function() {
        return this.lastname + ', ' + this.firstname;   
    }
}

var jim = {
    getFirstName: function() {
        return firstname;   
    }
}

_.extend(john, jane, jim);

console.log(john);

Reference:
http://underscorejs.org/docs/underscore.html
https://www.udemy.com/understand-javascript/learn/v4/t/lecture/2562700?start=0