JavaScript: Variables and Functions

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  • 1. JS  Variables  and  Func1ons   Jussi  Pohjolainen  Tampere  University  of  Applied  Sciences  
  • 2. Datatypes  •  Numbers  •  Boolean  •  String  •  Null,  undefined  •  Object  •  Func1on  
  • 3. Variable  scope  •  Global  and  local  variables  •  JS  does  not  have  block  statement  scope!   function test() { if(true) { var x = 5; } document.write(x); }•  This  works!  X  is  defined  in  the  scope  of  the   func1on  (or  globally)  
  • 4. Hois1ng  •  Variables  are  moved  on  top  of  the  func1on!  function test() { var x; if(true) { x = 5; } document.write(x);}
  • 5. Hois1ng  function test() { document.write(x); // Prints undefined! if(true) { var x = 5; }}
  • 6. Hois1ng  function test() { var x; document.write(x); // Prints undefined! if(true) { x = 5; }}
  • 7. So  what  happens  here?  var x = 10;function test() { document.write(x); if(true) { var x = 5; }}
  • 8. So  what  happens  here?  var x = 10;function test() { var x; // Overrides the global one.. document.write(x); // undefined if(true) { x = 5; }}
  • 9. Global  Objects  •  Global  variables  are  in  fact  proper1es  of  the   global  object!  •   In  web  pages  the  global  object  is  window  •  So   –  var  x  =  5  ó  window.x  =  5;  
  • 10. Objects  var Sales = "Toyota";function CarTypes(name) { if (name == "Honda") return name; else return "Sorry, we dont sell " + name + ".";}var car = { myCar: "Saturn", getCar: CarTypes("Honda"), special: Sales };document.write(car.myCar); // Saturndocument.write(car.getCar); // Hondadocument.write(car.special); // Toyota
  • 11. Basic  Func1on  function add(a, b){ return a+b;}alert(add(1,2));
  • 12. Func1on  as  Variable  var add = function(a, b){ return a+b;}alert(add(1,2));
  • 13. Func1on  as  Variable  var add=function theAdd(a, b){ return a+b;}alert(add(1,2)); // produces 3alert(theAdd(1,2)); // also produces 3