javascript

Chapter 4: Variables, Scope, and Memory
on obj1 , it can later be accessed from obj2 because they both point to the same object. Figure 4 - 3 shows
the relationship between the variables on the stack and the object on the heap.
Stack before copy
Heap
Object
obj1
(Object type)
Object
Stack after copy
Object
obj2
(Object type)
Object
obj1
Figure 4 - 3
(Object type)
Argument Passing
All function arguments in ECMAScript are passed by value. This means that the value outside of the
function is copied into an argument on the inside of the function the same way a value is copied from
one variable to another. If the value is primitive, then it acts just like a primitive variable copy, but if the
value is a reference, it acts just like a reference variable copy. This is often a point of confusion for
developers because variables are accessed both by value and by reference, but arguments are passed
only by value.
When an argument is passed by value, the value is copied into a local variable (a named argument or, in
ECMAScript, a slot in the arguments object). When an argument is passed by reference, the location of
the value in memory is stored into a local variable, which means that changes to the local variable are
reflected outside of the function. Consider the following example:
function addTen(num) {
num += 10;
return num;
}
var count = 20;
var result = addTen(count);
alert(count); //20 - no change
alert(result); //30
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