delete.js

//The delete operator deletes an object, an object's property, or an element at a specified index in an array. Syntax:
delete objectName;
delete objectName.property;
delete objectName[index];
delete property; // legal only within a with statement


//If the delete operator succeeds, it sets the property or element to undefined. 
//The delete operator returns true if the operation is possible; it returns false if the operation is not possible.
x = 42;
var y = 43;
myobj = new Number();
myobj.h = 4;    // create property h
delete x;       // returns true (can delete if declared implicitly)
delete y;       // returns false (cannot delete if declared with var)
delete Math.PI; // returns false (cannot delete predefined properties)
delete myobj.h; // returns true (can delete user-defined properties)
delete myobj;   // returns true (can delete if declared implicitly)