javascript datatype

javascript的data type可以分為(1) primitive type (2) reference type (objects)
primitive: fixed size in memory, ex: numbers, boolean values, null, undefined
reference(objects): can be of any length, ex: array, objects, functions.

var a = 3.14;  // Declare and initialize a variable
var b = a;     // Copy the variable's value to a new variable
a = 4;         // Modify the value of the original variable
alert(b)       // Displays 3.14; the copy has not changed

var a = [1,2,3];  // Initialize a variable to refer to an array
var b = a;        // Copy that reference into a new variable
a[0] = 99;        // Modify the array using the original reference
alert(b);         // Display the changed array [99,2,3] using the new reference