Javascript

Functions - may or may not return a value.

function declaration

function function_name(){
 // statements
};

var c = function_name();
console.log(c);

function expression

var function_name = function(){
 //statements
};

var c = function_name();
console.log(c);

Methods - when function is an object's property

var calc = {

add : function(a,b) {
          return a+b
          },

sub : function(a,b){
          return a-b
          }
}

calc => object
add,sub => method

calc.add(1,2);
calc.sub(3,2);

Constructors - when you add new keyword before a function and call it, it becomes a constructor that create instances.

function fruit(){
  var name,family;
  this.getName = function(){
      return name;
  };
  this.setName = function(value){
      name=value;
  };
}


var apple = new fruit();
apple.setName("Malus");
console.log(apple.getName());

function as a parameter

function f1(val){
    return val.toUpperCase();
}

function f2(val,passFunc){
    console.log(passFunc(val));
}

f2("small",f1);
// string, reference


Scope
global/public
local/private

global variable
- place a var statement outside any function
- omit var statement
local variable
- variables declared within a function

this parameter
refers to an object that's implicitly associated with function invocation

invocation as a function
- 'this' is bound to global object(window)
invocation as a method
- 'this' is bound to object
invocation as a constructor

Create JavaScript Object
object literal => similar to JSON format
var author ={
// variables
 firstName : "Megha",
 lastName : "Dureja",
 book : {
            title : "JS",
            pages : "172"
 }
// method
 meetingRoom : function(roomId){
    console.log("BookedRoom");
 }
};

console.log(author.lastName);
console.log(author.book.title);

object constructor
var author = new Object();

function constructor

prototype

function/prototype combination

singleton


Variable / Object

variable - container for data value
var car = "Polo";

Object - container for many value and methods to perform action
 <script>
var car = {
 type : "Polo",
 model : "500",
 color : "white"
 fullName : function(){
 return this.type + "" + this.model + "" +this.color;
 }
};
</script>

Hadoop Ecosystem

Hadoop Ecosystem = HDFS + MapReduce + Tools(Hive,Pig,HBase,Zookeeper,Flume,Sqoop,Oozie,Mahout)

Three modes
Local standalone mode - single JVM
pseudo distributed mode - separate JVM
fully distributed mode - multiple JVM

Hadoop Components
Namenode
Datanode
Secondary Namenode
JobTracker
TaskTracker

Configuration files
core-site.xml => location of namenode
hdfs-site.xml => replication factor
mapred-site.xml => location of jobtracker

hadoop dfs -ls
dfs -copyFromLocal
dfs put
dfs -cat
dfs -get