javascript intro

should write in last before closing of the body tag bec the function may not know about the buttons functionalities

var keyword
typeof  for getting the type of variable
var keyword is global
any variable that you create with keyword var that will be inside window object
any variable defined within function,will not be able to access outside.
window objects are common for all the files
document is part of window object

few selectors to locate object
1. document.getElementById()
2. document.getElementsByClassName()
3. document.getElementsByTagName

no class in javascript but there is object in javascript ,that is why it is called object based programming not obj. oriented programming.


guidelines
1. always recommended to start the first name of the file with "use strict" ----- will give errors of defining varibles of global
2. if u are using global variables then u (should) define in starting of the program.--ex- var a,b,c

**********css---- box-sizing:border-box   
tabindex


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                             mdn javascript
                             johnpapa
                             scotch.io
      risingstack.io
      
variable hoisting is done by javascript. means all variables with assignment will be declared in starting of program.


variable vs property
properties are attached to context whereas variables are attached are attached to context.
if a function 'a' defined with new inside function b then function a can acces b's var but b cannot acces properties of a;


closure ---- concept in which inner function will remember 

properties of an object are always key-value pair



longitude -77.696784  latitude-12.981225      https://www.latlong.net/


querySelector and querySelectorAll
event bubbling