Tag Archives: Computer programming

Does JavaScript undefined Equals undefined?

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Weird JS

Does "undefined" equals "undefined"?
Does JavaScript "undefined" equals "undefined"?

As you know sometimes JavaScript can be weird. Let’s see the following example and let’s try to answer the question: does “undefined” equals “undefined”. What do I mean?

First take a look at the following code.

var a;
var b = undefined;
 
// alerts "false"
alert(b == a);

Both a and b are undefined, but they are NOT equal. Now let’s see where it can become a problem.

We have an object with one member variable that is not defined.

var f1 = function()
{
	this.myvar;
};
 
var obj1 = new f1();

Now you’d like to know whether the object “b” has the property “myvar”. There are lots of examples online, but what’s the right way?
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Some Notes on the Object-oriented Model of PHP

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PHP 5 introduces interfaces and abstract classes. To become a little clearer, let us see their definitions.

Interfaces

Object interfaces allow you to create code which specifies which methods a class must implement, without having to define how these methods are handled.
Interfaces are defined using the interface keyword, in the same way as a standard class, but without any of the methods having their contents defined.
All methods declared in an interface must be public, this is the nature of an interface.

To implement an interface, the implements operator is used. All methods in the interface must be implemented within a class; failure to do so will result in a fatal error. Classes may implement more than one interface if desired by separating each interface with a comma.

Abstract Classes

PHP 5 introduces abstract classes and methods. Classes defined as abstract may not be instantiated, and any class that contains at least one abstract method must also be abstract. Methods defined as abstract simply declare the method’s signature – they cannot define the implementation.

When inheriting from an abstract class, all methods marked abstract in the parent’s class declaration must be defined by the child; additionally, these methods must be defined with the same (or a less restricted) visibility. For example, if the abstract method is defined as protected, the function implementation must be defined as either protected or public, but not private. Furthermore the signatures of the methods must match, i.e. the type hints and the number of required arguments must be the same. This also applies to constructors as of PHP 5.4. Before 5.4 constructor signatures could differ.

Some Cases

Now let’s do a quick experiment. According to the definition of interfaces we can define an interface and than an abstract class can implement this interface.
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Thing to Know About PHP Arrays

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Consider the following case. We have an array with identical keys.

$arr = array(1 => 10, 1 => 11);

What happens when the interpreter reaches this line of code? This is not a syntax error and it is completely valid. Very similar, but more interesting case is when we have an array of identical keys, where those identical keys are represented once as an integer and then as a string.

Keys in PHP arrays are not type sensitive, so pay attention when using them!
Keys in PHP arrays are not type sensitive, so pay attention when using them!

$arr = array(1 => 10, "1" => 11);

Now several questions arise. First of all, how many elements have this array? Two or one. This can be easily verified by checking what count() will return. Continue reading Thing to Know About PHP Arrays →

Powerful PHP: Less Known String Manipulation

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Yet another thing that’s great in PHP is the power you have when doing some string manipulation/operation. Here’s something that is really useful, but I think it remains a bit unknown. Let’s imagine you need to take the first (or whatever) character of a string. Most developers go to the obvious:

$str = 'hello world';
echo substr($str, 0, 1); // outputs "h"

But here’s something better and cleaner.

echo $str{0}; // outputs "h"

This code chunk return the first character of $str, but it can be used with the same success for any other character of the string. In my opinion this is more cleaner and its really syntactically self documented.

This approach can be useful when trying to check whether the first symbol for instance is “?” or “/”.

OOP JavaScript: Accessing Public Methods in Private Methods

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As you know in JavaScript when you define a variable with the special word “var” the scope of this variable is within the function. So when you simply wite “var a = 5” the variable named “a” has a global scope and can be accessed in any function in the global scope.

var a = 5;
 
function f() { return a; } // returns 5

Thus f will return the value of “a” which equals to 5. You can also change the value of the global variable in the function body.

var a = 5;
function f() { a = 10; return a; }
console.log(a); // equals to 10

Now after we call the function f the value of “a” will equal to 10. This is because we reference the global variable “a” into the function body without using the keyword “var”. This means that if you put the “var” keyword the variable “a” inside the function body is no longer the same variable as the variable defined outside the body. It becames “local” and it’s visible only inside the function.
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