JavaScript Advanced Programming (Third Edition) Chapter fourth variables, scope and memory issues

JavaScript variables can be used to hold two types of values: primitive type values and reference type values. Basic type values and reference type values have the following characteristics:

• The base type value occupies a fixed amount of space in memory and is therefore stored in the stack memory;
• Copying a base type value from one variable to another creates a copy of the value;
• The value of a reference type is an object that is stored in heap memory;
• A reference-type-worthy variable actually contains not the object itself, but a pointer to that object;
• Copying the value of a reference type from one variable to another is actually a pointer, so two variables end up pointing to the same object;
• Determine which base type a value can use the TypeOf operator, and determine which reference type can use the instanceof operator.

4.1.3 Passing parameters

1<script type= "Text/javascript" >2         functionAddten (num) {3num + = 10;4             returnnum;5         }6         7         varCount = 208         varresult =Addten (count);9alert (count);// -Tenalert (result);//Ten One  A</script>

1     <script type= "Text/javascript" >2         function  setName (obj) {3             Obj.name = "Nicholas"; 4         }        5         var New Object (); 6         setName (person); 7         alert (person.name);    // "Nicholas" 8     </script>

4.2.2 does not have a block level scope

 <script type= "Text/javascript" > function   add (NUM1, num2) { var  sum = num1 + return   sum;   var  result = Add (10, 20); //     30  alert (sum); //  because sum is not a valid variable, it causes the error  </script> 

 1  <script type= "Text/javascript" > 2  function   add (NUM1, num2) { 3  sum = num1 + num2;  4   sum;  5   6  var  result = Add (10, 20); // 30                 7  alert (sum); // 30  8  </script> 

1     <script type= "Text/javascript" >2         var color = "Blue"; 3         4         function GetColor () {5             return color; 6         }7         8         alert (GetColor ());  // "Blue"    9     </script>

1<script type= "Text/javascript" >2         varcolor = "Blue";3         4         functionGetColor () {5             varcolor = "Red";6             returncolor;7         }8         9Alert (GetColor ());//"Red"Ten</script>

JavaScript Advanced Programming (Third Edition) Chapter fourth variables, scope and memory issues