anandmnair / documents

java-script-demo

variables

* var x = 10  vs   x = 10

function fun() {
  var x = 10;
  a = 10;
}

'x' -> function scope : x with in function will store in function sope

'a' -> window scope : a (with out 'var' ) in function will not be part of function scope, it will be part of wiindow object.

equals ( = | == | === )

* var x=5  , var y="5" .   x==y -> true .   x===y -> false

variables scopes

• global variables : stored iin window object
• functional variables

* java script follows functional scopping not block scopping

var name="anand";
if(name=="anand") {
  var gender = "male";
}
console(name);
console(gender);  // accessable even outside the if scope

function scopeDemo() {
  var name="anand";
  if(name=="anand") {
    var gender = "male";
  }
  console(name);
  console(gender);  // accessable even outside the if scope
}

console(gender);  // runtime exception : gender is reading without write operation

var a=10;
function myFunc() {
  var b=20;
  var func = function() {
    var c=30;
    console.log(a+b+c);
  };
  console(a+b);
  func();
}

myFunc();

// Output
// 30  (a+b)
// 60  (a+b+c)

IIFE

Immediately Invoked Function Expression

 - Always make a variable with in functional scope 
 - anonymous function

(function() {
 console.log("hello anand");
})();     // this anonymous function calling at the same point of declaration - > IIFE  

var fun = (function() {        //save funtion to fun variable
 console.log("hello anand");
});
fun(); // calling anonymous function from the reference var

Compilation & Interpretation

• Compiler : only allocates the valriable to its scopes (Does not assign)
• Interpretor : Do the allocations

var myName="Anand";
finction greet(name) {
  c=10;
  console.log("Hello " + name);
}
greet(myName);

Global Scope : myName , greet , c

Function Scope : name

Javascript Hoisting