473,714 Members | 2,470 Online
Bytes | Software Development & Data Engineering Community
+ Post

Home Posts Topics Members FAQ


I've noticed some confusion about the use of the this keyword. It is set for
each invocation of a function. There are 4 basic calling patterns:

1. foo()
2. bar.foo()
3. new foo()
4. foo.apply(bar)

In the first case, foo's this will be set to the global object (aka window).
This is an acceptable behavior for global functions, although null would have
been a better choice. This is very unfortunate behavior for inner functions,
because it makes it harder to write helper functions within a method.

In this second case, foo's this will be set to the bar object. This supports
calls to methods. Unlike some other languages (like Java), the use of this
within a method must be explicit.

In the third case, foo's this will be set to a new object that is linked to
foo.prototype. This supports constructor functions. Note that constructor
function must be called with the new prefix. If the new prefix is missing,
it degenerates to the first case, and the constructor will clobber the global

In the fourth case, foo's this will be bar. This makes it possible to call a
function that is not a method of the object as though it is a method of the


Jul 20 '05 #1
1 1505
Douglas Crockford wrote:
I've noticed some confusion about the use of the this keyword. It is set for
each invocation of a function. There are 4 basic calling patterns:

1. foo()
2. bar.foo()
3. new foo()
4. foo.apply(bar)


In the fourth case, foo's this will be bar. This makes it possible to call a
function that is not a method of the object as though it is a method of the

Have you ever heard of this 4th case being called "environmen tal
acquisition"? There's a paper on it at:


There was also a python and smalltalk usenet thread about it a couple of
years ago; python because apparently Zope makes use of this concept. I
mentioned Javascript does too and that was the end of the thread ;)
Jul 20 '05 #2

This thread has been closed and replies have been disabled. Please start a new discussion.

Similar topics

by: James | last post by:
I have a from with 2 fields: Company & Name Depening which is completed, one of the following queries will be run: if($Company){ $query = "Select C* From tblsample Where ID = $Company Order By Company ASC";
by: Scott D | last post by:
I am trying to check and see if a field is posted or not, if not posted then assign $location which is a session variable to $location_other. If it is posted then just assign it to $location_other I keep getting "Notice: Undefined index: location_other" referring to (!($_POST)) { $location_other = $location; } else
by: Nick | last post by:
Can someone please tell me how to access elements from a multiple selection list? From what ive read on other posts, this is correct. I keep getting an "Undefined variable" error though... Form page************************************************************ <form action="/process.php" method="get" name="formOne" id="formOne"> <select name="owner" size="6" multiple id="owner"> <option value="one">one</option> <option...
by: Alexander Ross | last post by:
I have a variable ($x) that can have 50 different (string) values. I want to check for 7 of those values and do something based on it ... as I see it I have 2 options: 1) if (($x=="one") || ($x=="two") || ... || ($x=="seven")) ... or 2) switch ($x){ case("one"):
by: Dan Foley | last post by:
This script runs fine, but I'd like to know why it's so slow.. Thanks for any help out there on how i can make it faster (it might take up to 5 min to write these 3 export files whith 15 records each!!!) Dan ==================== <style> body, table, tr, td { font-family: 'verdana'; font-size: 12px;
by: Lee Redeem | last post by:
Hi there I've created abd uploaded this basic PHP script: <html> <head> <title>PHP Test</title> </head> <body> <H1 align="center">
by: christopher vogt | last post by:
Hi, i'm wondering if there is something like $this-> to call a method inside another method of the same class without using the classname in front. I actually use class TEST { function func1()
by: Phil Powell | last post by:
Ok guys, here we go again! SELECT s.nnet_produkt_storrelse_navn FROM nnet_produkt_storrelse s, nnet_produkt_varegruppe v, nnet_storrelse_varegruppe_assoc sv, nnet_produkt p WHERE s.nnet_produkt_storrelse.id = sv.nnet_produkt_storrelse_id AND sv.nnet_produkt_varegruppe_id = v.nnet_produkt_varegruppe_id AND sv.nnet_produkt_varegruppe_id IN ( SELECT nnet_produkt_varegruppe_id FROM nnet_produkt_varegruppe
by: Michel | last post by:
a site like this http://www.dvdzone2.com/dvd Can you make it in PHP and MySQL within 6 weeks? If so, send me your price 2 a r a (at) p a n d o r a . b e
by: Maciej Nadolski | last post by:
Hi! I can`t understand what php wants from me:( So: Cannot send session cache limiter - headers already sent (output started at /home/krecik/public_html/silnik.php:208) in /home/krecik/public_html/silnik.php on line 251 Line 208: print ( "error: " . mysql_error()); Line 251: session_register("uprawnienia", "zalogowany"); I can understand that sth, is wrong in line 251 after line 208 and it is logical to
by: marktang | last post by:
ONU (Optical Network Unit) is one of the key components for providing high-speed Internet services. Its primary function is to act as an endpoint device located at the user's premises. However, people are often confused as to whether an ONU can Work As a Router. In this blog post, we’ll explore What is ONU, What Is Router, ONU & Router’s main usage, and What is the difference between ONU and Router. Let’s take a closer look ! Part I. Meaning of...
by: jinu1996 | last post by:
In today's digital age, having a compelling online presence is paramount for businesses aiming to thrive in a competitive landscape. At the heart of this digital strategy lies an intricately woven tapestry of website design and digital marketing. It's not merely about having a website; it's about crafting an immersive digital experience that captivates audiences and drives business growth. The Art of Business Website Design Your website is...
by: agi2029 | last post by:
Let's talk about the concept of autonomous AI software engineers and no-code agents. These AIs are designed to manage the entire lifecycle of a software development project—planning, coding, testing, and deployment—without human intervention. Imagine an AI that can take a project description, break it down, write the code, debug it, and then launch it, all on its own.... Now, this would greatly impact the work of software developers. The idea...
by: isladogs | last post by:
The next Access Europe User Group meeting will be on Wednesday 1 May 2024 starting at 18:00 UK time (6PM UTC+1) and finishing by 19:30 (7.30PM). In this session, we are pleased to welcome a new presenter, Adolph Dupré who will be discussing some powerful techniques for using class modules. He will explain when you may want to use classes instead of User Defined Types (UDT). For example, to manage the data in unbound forms. Adolph will...
by: TSSRALBI | last post by:
Hello I'm a network technician in training and I need your help. I am currently learning how to create and manage the different types of VPNs and I have a question about LAN-to-LAN VPNs. The last exercise I practiced was to create a LAN-to-LAN VPN between two Pfsense firewalls, by using IPSEC protocols. I succeeded, with both firewalls in the same network. But I'm wondering if it's possible to do the same thing, with 2 Pfsense firewalls...
by: adsilva | last post by:
A Windows Forms form does not have the event Unload, like VB6. What one acts like?
by: 6302768590 | last post by:
Hai team i want code for transfer the data from one system to another through IP address by using C# our system has to for every 5mins then we have to update the data what the data is updated we have to send another system
by: muto222 | last post by:
How can i add a mobile payment intergratation into php mysql website.
by: bsmnconsultancy | last post by:
In today's digital era, a well-designed website is crucial for businesses looking to succeed. Whether you're a small business owner or a large corporation in Toronto, having a strong online presence can significantly impact your brand's success. BSMN Consultancy, a leader in Website Development in Toronto offers valuable insights into creating effective websites that not only look great but also perform exceptionally well. In this comprehensive...

By using Bytes.com and it's services, you agree to our Privacy Policy and Terms of Use.

To disable or enable advertisements and analytics tracking please visit the manage ads & tracking page.