Coder's Corner

Listen a property for changes in JavaScript

2011-12-29T01:12:00.000-08:00

There are two very interesting functions of Object in JavaScript - watch and unwatch. These two methods could be used to track changes of some specific properties of any Object. watch() watches for a property of an Object, if a value is assigned to that property, it will run registered function.

Example,
Here i have an Object obj1 which has property myprop with value 1. Later watch method is used to register myprop property, if any changes/assignment is made to that property appropriate function is called. In this case whenever myprop of obj1 is assigned a value function is executed and alerts a msg.

obj1 = {myprop:1};

// start watch on obj1.myprop from here
obj1.watch("myprop",
function (prop_name, oldval, newval) {
alert("obj1." + prop_name + " changed from " + oldval + " to " + newval)

return newval;
});

// assign new values
obj1.myprop = 2;
obj1.myprop = 3;
obj1.myprop = 4;

// unwatch on obj1.myprop from here
obj1.unwatch("myprop");

// assign new values

obj1.myprop = 5;

obj1.myprop = 6;
obj1.myprop = 7;

Tips on coding style..

2011-08-15T06:38:00.001-07:00

Well his post will be regarding some tips on coding style. I googled about this topic, checked many sites, read many posts, finally made a list on them...

Meaningful names to variables -- i.e., name them meaningfully so that it corresponds as closely as possible to verbal description of its usage.

Maintain a labbook from the beginning of a project to the end.
Code each variable so that it corresponds as closely as possible to a verbal description of the substantive hypothesis the variable will be used to test.
Errors in code should be corrected where they occur and the code re-run.
Separate tasks related to data-manipulation vs data-analysis into separate files.
Each program should perform only one task.
Do not try to be as clever as possible when coding. Try to write code that is as simple as possible.
Each section of a program should perform only one task.
Use a consistent style regarding lower and upper case letters.
Use variable names that have substantive meaning.
Use variable names that indicate direction where possible.
Use appropriate white-space in your programs, and do so in a consistent fashion to make them easy to read.
Include comments before each block of code describing the purpose of the code.
Include comments for any line of code if the meaning of the line will not be unambiguous to someone other than yourself.
Rewrite any code that is not clear.
Verify that missing data is handled correctly on any recode or creation of a new variable.
After creating each new variable or recoding any variable, produce frequencies or descriptive statistics of the new variable and examine them to be sure that you achieved what you intended.
When possible, automate things and avoid placing hard-wired values (those computed `by-hand') in code.

Oldest computer???

2011-07-29T06:47:00.000-07:00

Which is the oldest computer??

Well some would say ENIAC, others would say Colossus, what ever it is, im sure its not my computer :) because i just purchased it, didnt invent it :)

The Answer is : "Antikythera"

It is an ancient mechanical computer which was being in use around 200BC (around 2000 years ago!!!). This device has been recovered from Antikythera Wreck (near greek island called crete), hence it gets its name "Antikythera". It is figured out that it was being used for two purposes, Astronomical and Astrological purposes. This device was used by greek astronomers for their research works!

Above is the picture of the recovered Antikythera. Scientists say, there are large number interconnected gears and is very complicated than a modern swiss watch!!. This device was recovered in 1900-1901. It took around 70 years to understand the complete inner workings of the Antikythera. In 1974, Price published a paper "Gears from the Greeks: the Antikythera mechanism — a calendar computer from ca. 80 BC", where he explained the inner working of the device. Based on these existing information, attempts are being made to build a replica of it.

Below are some of the pictures of the actual device,

The following are the pictures of reconstructed device,

You can watch videos on net for more info, some video links

(All images are copyrighted, actual owner of the image holds rights over the image)

First post

2011-07-29T05:48:00.000-07:00

Well guys this will be my blog to share some cool stuffs related to computers.

My first post will be soon..!