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  Undefined property or variable in JavaScript

JavaScript is a weak type language, and also you can use a variable or property where it's undefined. If we don't have correct ways to check whether a property or variable is defined, we may get unexpected results when we try to access the,. How can we check whether a property or variable is undefined? This is actually a somewhat tricky question. Let's start off with some facts about undefined and then see what kind of function is consistent with the ones we care about. JavaScript attaches type...

   Property,Undefined,Array,JavaScript     2014-07-24 06:56:07

  this in JavaScript

this is a keyword in JavaScript. It refers to an internal object created automatically when a function executes, it can only be used in a function. For example:        function test(){ 　　　　this.x = 1; 　　}The this keyword will change when a function is called in different situations. However, the general rule is : this refers to the object which calls the function.Next we discuss the use of this in 4 different situatio...

   this,keyword,use,JavaScript     2012-05-05 12:47:37

  Tips and tricks about JavaScript from Google

JavaScript is now a very popular client side language. It's flexible, powerful but easy to make mistakes. So good programming style is better for you to write efficient and readable JavaScript codes. Here are some tips and tricks about JavaScript from Google. True and False Boolean Expressions The following are all false in boolean expressions: null undefined '' the empty string 0 the number But be careful, because these are all true: '0' the string [] the empty array {}&n...

   JavaScript, Google, Coding standard     2013-02-26 23:11:03

  Format JSON data on Ubuntu

JSON now becomes a very popular data format because of its simplicity and light-weight. Nowadays many RESTful APIs will offer a choice of exchanging JSON data between the server and client. Sometimes the data may not be formatted and it cannot be easily read by human beings. It's frequently desired that the unformatted JSON data should be formatted before read. Today we will show a few ways to format JSON data on Ubuntu. Assume we have a json file test.json with below content. { "title": "Test"...

   RUBY,PYTHON,NODEJS,JSON,JQ,PERL,LINUX,UBUNTU,YAJL     2016-08-17 11:05:09

  this in JavaScript in detail

this in JavaScript is always confusing, it is one of the most frequently seen traps in JavaScript. this is not a good design in JavaScript(You can refer some other design flaws of JavaScript here), since it's lazy binding feature, it can be a global object, the current object or.... Some people even avoid using this in JavaScript. Actually if you master how this works, then you will know how to stay away from these traps. Let's take a look at what this points to in below situations. 1. In global...

   JavaScript,this,bind     2013-05-09 18:35:12

  When Should Open Source Be Written Into Law?

As a systems administrator, I tend to think about source code and computing platform in large numbers. Computers however are getting smaller and more powerful, and the reality of computers that we put in or on our body as a normal daily routine is coming closer, and for many is already here. When our safety, our liberty, and our sense of humanity are tied to programmable devices, should we not only hope, but expect that we should have the right to examine how these devices function? Last ...

   Software,Open source,Time,Law     2012-01-28 07:23:09

  Recursive class initialization in Java

When a Java class is referenced and initialized, it has to go through the loading and linking first. Once the loading and linking complete successfully. The class will be initialized. The static variables and constant variables will be initialized during this process. Once the class is initialized, it is ready for use. If when class A is initialized and it is referencing a class B, the class B will also get initialized. But what will happen if class B is referencing class A as well? This is call...

   Java,JVM,class initialization,static final     2015-04-15 21:04:29

  What's on your Learning List?

How do you track and decide what topics you want to spend time learning? For a while, I didn’t have a real good solution. Something would trigger me to remember “Oh yeah! I really wanted to learn more about that”. I would spend the evening doing busy learning - it seemed like I was learning but I really wasn’t. Instead of trying to do Deliberate Practice, I’d fool myself into thinking I was investing my time wisely by reading blog posts and examples but no...

   Learning list,Conscious,Study,Programming     2011-12-05 12:44:39

  JavaScript interview questions

This post will cover the JavaScript questions I have encountered and have seen during my programming career. They will mainly focus on vanilla JavaScript though there are lots of excellent frameworks out there and many people are using them in their daily work. this keyword this keyword is an very important but easy to confuse concept in JavaScript since it is always referring to the calling object of the function. 1. What will be the output of below code snippet? function User(name) { this....

   JAVASCRIPT,ALGORITHM,THIS,CLOSURE     2019-03-09 07:05:46

  4 asynchronous programming methods in JavaScript

You may know the execution environment of JavaScript is single threaded. The so called single thread means only one task can be running at any time, if there are many tasks, they need to be in a queue and wait for the previous task to be completed. The advantage of this mode is it's easy to implement and the execution environment is relative simple; the disadvantage is that if one task takes long time, the tasks following it must wait in the queue and this will delay other tasks consequently. Th...

   JAVASCRIPT,ASYNCHRONOUS PROGRAMMING, EVENT MODEL,PROMISE     2012-12-25 00:55:47

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