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Function class

The function

doAdd()

adds 10 to a number only if there is one argument; if there are two arguments,

they are simply added together and returned. So

doAdd(10)

outputs

“20”

whereas

doAdd(30,20)

out-

puts

“50”

. It’s not quite as good as overloading, but it is a sufficient workaround for this ECMAScript

limitation.

The Function class

Perhaps the most interesting aspect of ECMAScript is that functions are actually full-fledged objects.

Function

class represents each and every function a developer defines. The syntax for creating a

function using the

Function

class directly is as follows:

var

function_name

= new Function(

argument1

argument2

,..,

argumentN

function_body

);

In this form, each of the function arguments is one parameter, with the final parameter being the func-

tion body (the code to execute). Each of these parameters must be a string. Remember this function?

function sayHi(sName, sMessage) {

alert(“Hello “ + sName + “,” + sMessage);

}

It can also be defined like this:

var sayHi = new Function(“sName”, “sMessage”, “alert(\”Hello \” + sName + \”, \” +

sMessage + \”);”);

Admittedly, this form is a little bit harder to write because of the nature of strings, but understand that

functions are just reference types and they always behave as if using the

Function

class explicitly cre-

ated for them. Remember this example?

function doAdd(iNum) {

alert(iNum + 100);

}

function doAdd(iNum) {

alert(iNum + 10);

}

doAdd(10); //outputs “20”

As you remember, the second function overrides the first, making

doAdd(10)

output

“20”

instead of

“110”

. This concept becomes a whole lot clearer if this block is rewritten as follows:

doAdd = new Function(“iNum”, “alert(iNum + 100)”);

doAdd = new Function(“iNum”, “alert(iNum + 10)”);

doAdd(10);

Looking at this code, it is clear that the value of

doAdd

has changed to point to a different object. Yes,

function names are just reference values pointing to a function object and behave just as other pointers

do. It is even possible to have two variables point to the same function:

ECMAScript Basics

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