NODEJS TIPS

node-tips.js

//******************************************************************
// Steps to set nodejs, expressjs and grunt:
// 1. Install nodejs
//    $ sudo npm install nodejs
// 2. Install expressjs//# 3. Install grunt-cli
// 5. Create a project using express (building a skeleton directory)
// 6. Install grunt
// 7. Create Package folder
// 8. Run grunt command
// 9. Create basic create and clean tasks
//******************************************************************

// DEBUGGING DOM VIA PROTRACTOR:
// $ node_modules/protractor/bin/elementexplorer.js https://localhost/#/page1

//*****************
// CONTEXT vs SCOPE
//*****************
// Every function invocation has both a scope and a context associated with it.
// Fundamentally, scope is function-based while context is object-based. In other words:
// * Scope pertains to the variable access of a function when it is invoked and is unique to each invocation.
// * Context is always the value of the this keyword which is a reference to the object that “owns” the currently executing code.

//**********************
// EVAL vs CALL vs APPLY
//**********************
// Define 2 objects, that will only be called by other functions.
var person1 = {name: 'Marvin', age: 42, size: '2xM'}
var person2 = {name: 'Zaphod', age: 4200000000, size: '1xS'}

// Define 2 methods, that will run into one context of different function.
var sayHello = function () {
  console.log('Hello, ' + this.name + ' -- ' + this.age);
};

var sayGoodBye = function () {
  console.log('GoodBye, ' + this.name);
};

// Wwill give an error because:
// both functions rely on their scope for the 'this.name' data,
// and calling them without explicit scope will just run them in the scope of the current window.
sayHello();
sayGoodBye();

// All next 4 lines do exactly the same thing.
// The sayHello or sayGoodBye will run in the scope of either person1 or person2.
sayHello.call(person1);
sayGoodBye.call(person2);

sayHello.apply(person1);
sayGoodBye.apply(person2);

/*
 * Note:
 * Both call and apply perform very similar functions: 
 * they execute a function in the context, or scope, of the first argument that you pass to them. 
 * Also, they're both functions that can only be called on other functions.
 */

// The eval() function evaluates or executes an argument.
// If the argument is an expression, eval() evaluates the expression.
// If the argument is one or more JavaScript statements, eval() executes the statements.
var x = 10;
var y = 20;
var a = eval("x * y") + "<br>";
var b = eval("2 + 2") + "<br>";
var c = eval("x + 17") + "<br>";

var res = a + b + c;

// The result of res will be:
200
4
27

//**********************************************************
// SELF EXECUTING ANONYMOUS FUNCTIONS (IIFE or SEAF pattern)
//**********************************************************
//ExampleS:
// Creates a function object
var f1 = (function() { alert('foo'); }); 

// Creates a function object and executes it immediately
var f2 = (function() { alert('foo'); })(); 

// Allows 'alert('foo')' to be executed immediately, as if it was just written inline, 
// but also within its own scope so as not to affect the global namespace 
// (and thus potentially interfere with or be interfered with by, other scripts).

// The difference is that f1 gives you a function object. f2 creates and invokes an anonymous function.
// By using an anonymous function in this manner you ensure it's only executed once.

// Example:
var counter = (function(){
  var i = 0;

  return {
    get: function(){
      return i;
    },
    set: function( val ){
      i = val;
    },
    increment: function() {
      return ++i;
    }
  };
}());

// 'counter' is an object with properties, which in this case happen to be methods.
counter.get(); // 0
counter.set( 3 );
counter.increment(); // 4
counter.increment(); // 5