Javascript Scope. Most languages with C syntax have block scope. All variables defined in a block ( curly braces ) are not visible from outside of the block. Unfortunately, JS does not have block scope, even though its block syntax suggests that it does. JS has function scope. That means that the parameters and variables defined in a function ar…

sope.js

var foo = function(){ 
  var a = 3
     ,b = 5;
     
  var bar = function(){
    var b = 7
        ,c = 11;
        
    //Right here: a == 3, b == 7 and c == 11
    
    a += b + c
    
    //Now, a == 21, b == 7, and c == 11
  };
  
  //Here a == 3, b == 5, and c is undefined
  
  bar(); //invoke the bar function
  
  //Finally, a == 21, b == 5.  
  
  //Notice that "c" is out of the scope here, so when the bar() function assigned c, 
  //the outer function couldn't get that value.
  //However, since a was in the scope of the outer function, the bar function could modify it.
  
  
}