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Larry Battle

Javascript Binary Operations - the easy way - 1 views

bateru.com/...binary-operations-the-easy-way

Javascript programming development scripting web bitwise operations

shared by Larry Battle on 16 Mar 11 - No Cached
  • Larry Battle on 16 Mar 11
     
    A Simple Guide for binary operations in javascript.
Javier Neira

Perfection kills » Understanding delete - 3 views

perfectionkills.com/understanding-delete

javascript delete tutorial

shared by Javier Neira on 11 Jan 10 - Cached
yc c liked it
  • All because it’s not possible to delete variables in Javascript. At least not when declared in such way.
  • It’s almost as if Firebug follows some other rules of deletion. It is Firebug that has led Stoyan astray! So what is really going on here?
  • we need to understand how delete operator works in Javascript: what exactly can and cannot be deleted and why.
  • ...35 more annotations...
  • var o = { x: 1 }; delete o.x; // true o.x; // undefined
  • var x = 1; delete x; // false x; // 1
  • function x(){} delete x; // false typeof x; // "function"
  • Note that delete only returns false when a property can not be deleted.
  • variable instantiation and property attributes
  • Global code, Function code and Eval code.
  • When a source text is treated as a Program, it is executed in a global scope, and is considered a Global code.
  • Anything that’s executed directly within a function is, quite obviously, considered a Function code. In browsers, content of event attributes (e.g. <p onclick="...">) is usually parsed and treated as a Function code.
  • text that’s supplied to a built-in eval function is parsed as Eval code. We will soon see why this type is special.
  • And now that we know the difference between property assignment and variable declaration — latter one sets DontDelete, whereas former one doesn’t — it should be clear why undeclared assignment creates a deletable property:
  • As you can see, execution contexts can logically form a stack. First there might be Global code with its own execution context; that code might call a function, with its own execution context; that function could call another function, and so on and so forth. Even if function is calling itself recursively, a new execition context is being entered with every invocation.
  • Every execution context has a so-called Variable Object associated with it. Similarly to execution context, Variable object is an abstract entity, a mechanism to describe variable instantiation. Now, the interesing part is that variables and functions declared in a source text are actually added as properties of this Variable object.
  • When control enters execution context for Global code, a Global object is used as a Variable object. This is precisely why variables or functions declared globally become properties of a Global object:
  • The behavior is actually very similar: they become properties of Variable object. The only difference is that when in Function code, a Variable object is not a Global object, but a so-called Activation object. Activation object is created every time execution context for Function code is entered.
  • and a special Arguments object (under arguments name). Note that Activation object is an internal mechanism and is never really accessible by program code.
  • within Eval code are created as properties of calling context’s Variable object. Eval code simply uses Variable object of the execution context that it’s being called within:
  • Now that it’s clear what happens with variables (they become properties), the only remaining concept to understand is property attributes. Every property can have zero or more attributes from the following set — ReadOnly, DontEnum, DontDelete and Internal. These attributes serve as sort of flags — an attribute can either exist on a property or not. For the purposes of today’s discussion, we are only interested in DontDelete.
  • When declared variables and functions become properties of a Variable object — either Activation object (for Function code), or Global object (for Global code), these properties are created with DontDelete attribute. However, any explicit (or implicit) property assignment creates property without DontDelete attribute. And this is essentialy why we can delete some properties, but not others:
  • Special arguments variable (or, as we know now, a property of Activation object) has DontDelete. length property of any function instance has DontDelete as well:
  • As you might remember, undeclared assignment creates a property on a global object.
  • Execution context When ECMAScript code executes, it always happens within certain execution context.
  • Variables declared within Eval code are actually created as properties without DontDelete:
  • This interesting eval behavior, coupled with another aspect of ECMAScript can technically allow us to delete non-deletable properties. The thing about function declarations is that they can overwrite same-named variables in the same execution context:
  • Note how function declaration takes precedence and overwrites same-named variable (or, in other words, same property of Variable object). This is because function declarations are instantiated after variable declarations, and are allowed to overwrite them
  • If we declare function via eval, that function should also replace that property’s attributes with its own. And since variables declared from within eval create properties without DontDelete, instantiating this new function should essentially remove existing DontDelete attribute from the property in question, making that property deletable (and of course changing its value to reference newly created function).
  • Unfortunately, this kind of spoofing doesn’t work in any implementation I tried. I might be missing something here, or this behavior might simply be too obscure for implementors to pay attention to
  • this.x = 1; delete x; // TypeError: Object doesn't support this action
  • var x = 1; delete this.x; // TypeError: Cannot delete 'this.x'
  • It’s as if variable declarations in Global code do not create properties on Global object in IE.
  • Not only is there an error, but created property appears to have DontDelete set on it, which of course it shouldn’t have:
  • “The global variable object is implemented as a JScript object, and the global object is implemented by the host.
  • Note how this and window seem to reference same object (if we can believe === operator), but Variable object (the one on which function is declared) is different from whatever this references.
  • delete doesn’t differentiate between variables and properties (in fact, for delete, those are all References) and really only cares about DontDelete attribute (and property existence).
  • The moral of the story is to never trust host objects.
  • Few restrictions are being introduced. SyntaxError is now thrown when expression in delete operator is a direct reference to a variable, function argument or function identifier. In addition, if property has internal [[Configurable]] == false, a TypeError is thrown:
mahesh 1234

Android Tutorial - Javatpoint - 0 views

www.javatpoint.com/android-tutorial

shared by mahesh 1234 on 24 Dec 13 - No Cached
  • mahesh 1234 on 24 Dec 13
     
    Android Tutorial. Android is a software package containing linux based operating system for mobile devices such as tablet computers, smartphones etc, middleware and key mobile applicaitons.
Javier Neira

Debugging Tools for Windows - Overview - 0 views

www.microsoft.com/...default.mspx

debug windows microsoft tools

shared by Javier Neira on 10 Jun 09 - Cached
  • Javier Neira on 10 Jun 09
     
    Provides links and information about tools, downloads, and recommended techniques for debugging drivers for Windows operating systems.">http://www.microsoft.com/MSCOM/MNP2/Schemas
Ivan Pavlov

Classes.Big Number - 0 views

jsfromhell.com/bignumber

javascript

shared by Ivan Pavlov on 16 Sep 08 - Cached
  • Offers a extremely high precision level to make mathematical operations. For integers there is no limits and for floating point numbers, the class allows setting the maximum precision.
Ivan Pavlov

JNEXT - JavaScript Native Extensions - 0 views

jnext.org

javascript

shared by Ivan Pavlov on 06 Oct 08 - Cached
  • JNEXT is an open source (triple MPL, GPL, LGPL license), small footprint, cross platform and cross browser framework for extending Web browser Javascript (for more background and motivation check this blog entry). With JNEXT it is possible to utilize existing Web browsers to host full and self contained applications that do not depend on external Web servers for the application logic (although they are free to make use of them). This is acheived by enabling Javascript controlled access to the full range of native operating system resources (such as TCP/UDP sockets, files, databases, threads etc).
Ivan Pavlov

oni - structured concurrency - 0 views

www.croczilla.com/oni

javascript concurrency

shared by Ivan Pavlov on 04 Sep 09 - Cached
  • Oni is a framework for managing the control flow of concurrent applications. There are two central ideas to Oni: To make concurrent actions composable by implementing 'pseudo-sequential' control structures with which asynchronous actions can be choreographed in the same way in which traditional sequential control structures are used to choreograph conventional synchronous actions. Ok, I'm not sure I even understand that myself. But please read on anyway :-) To leverage the facilities of a "host language" rather than implement a complete programming language from scratch. Oni can be implemented as a set of functions ("Oni operators") in a suitable host language, such as JavaScript or C++ (any reasonable language will do). Our current implementation, dubbed Oni/JS, is in JavaScript, targeted at in-browser use (should work in any modern browser - FF, Chrome, Safari, IE, ...). Oni requires no preprocessing or precompilation; an Oni program is a just an expression in the host language.
  • Ivan Pavlov on 04 Sep 09
     
    Oni is a framework for managing the control flow of concurrent applications.
Javier Neira

12 Tips to improve your jQuery code | Geekology - 2 views

www.geekology.co.za/...-tips-improve-your-jquery-code

jquery bestpractices tips javascript

shared by Javier Neira on 30 Oct 09 - Cached
  • DOM manipulation is one of the slowest operations JavaScript (and hence, jQuery) can perform.
  • Use IDs instead of classes in selectors
  • When you need to perform multiple methods on elements, jQuery can chain those methods together.
  • ...2 more annotations...
  • 11. Use jQuery’s noConflict() method to rename the jQuery object when working with multiple frameworks: Many JavaScript frameworks use the “$” symbol to reference the framework. If you use multiple frameworks in your project, use the jQuery.noConflict() method to release the “$” object and assign jQuery to a custom-named object:
  • 12. Use shorthand for the $(document).ready() event:
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