JavaScript Tutorials - Herong's Tutorial Examples - 2.33, by Herong Yang
Function Parameters Are Passed as Local Copies
This section provides a quick description of how primitive parameters and object parameters are all passed as local copies of whatever original variables store.
As shown in a previous section, JavaScript function call follows two rules: primitive parameters are passed by value and object parameters are passed by reference.
But actually, both rules are derived from a single rule: parameters are passed as local copies of whatever original variable store:
Notice that the above explanation uses these assumptions:
Saying that parameters are passed as local copies is actually more accurate, because passing parameters by reference is a very different programming feature.
Taking VBScript as an example, it supports the "ByRef" keyword to allow you to pass a function parameter as true reference for any data types, including primitive types. A VBScript function will not create a local copy of a "ByRef" parameter. It will use the "ByRef" parameter as an alias of the original variable.
The following VBScript code will swap the original variables by using "ByRef" parameters:
vFirst = "Dog" vSecond = "Cat" Call SwapByRef(vFirst, vSecond) document.writeln(" After Sub: " & vFirst & " | " & vSecond) Sub SwapByRef(ByRef vLeft, ByRef vRight) vTemp = vLeft vLeft = vRight vRight = vTemp End Sub
If you try to write a JavaScript function to swap two objects, you will definitely fail. See the next section for my examples.
Table of Contents
ECMAScript Language Specification and JavaScript Dialects
Data Types, Variables and Expressions
Creating, Accessing, and Manipulating Arrays
►Defining and Calling Functions
Defining Your Own Functions - Example
Calling Your Own Functions - Example
Passing Parameters by Value or by Reference
►Function Parameters Are Passed as Local Copies
Function Parameters Are Passed as Local Copies - Example
Global and Local Variables - Scope Rules
Collision of Global and Local Variables - Examples
"return" Statement and Return Value
Web Browser Supporting JavaScript
Server-Side and Client-Side Web Scripting
Defining Your Own Object Types
Inheritance of Properties and Methods through the Prototype Object Chain
'jrunscript' - JavaScript Shell Command from JDK
Using Functions as "Function" Objects
Introduction to Built-in Object Types
W3C's Document Object Model (DOM) Specifications