javascript

Chapter 22: The Evolution of JavaScript
ECMAScript 3.1 also adds two new properties to each function: name and parameters . The name
property contains the name of the function as it appears when using a function declaration, and the
parameters property is an array of strings containing the named function properties. Here is an
example:
function add(num1, num2){
return num1 + num2;
}
alert(add.name); //”add”
alert(add.parameters[0]);
alert(add.parameters[1]);
//”num1”
//”num2”
These properties help to inspect functions for debugging purposes. Note that if the function is
anonymous, its name property will be an empty string.
The last change to functions is with the arguments object. In ECMAScript 3, the arguments object was
array - like, having numeric indices and a length property, but it was not actually an instance of Array .
ECMAScript 3.1 makes the arguments object officially into an instance of Array , allowing usage of all
array methods for processing arguments.
Changes to Other Types
There are some additional changes involving other data types in ECMAScript 3.1. One of the major
issues in ECMAScript 3 was not being able to determine if an object was an array. The big problem was
with arrays being passed from one frame to another. Since each frame has its own global object, each also
had its own Array constructor, so an array from one frame wasn ’ t necessarily an instance of Array in
another frame — clearly, this led to confusion.
ECMAScript 3.1 introduces the Array.isArray() method to determine if an object is, in fact, an array.
This method accepts a single argument, which is the object to check, and returns true if the object is
determined to be an array. This works regardless of the object ’ s origin and is designed specifically to
work around the cross - frame array identification problem. The method is used as follows:
var nums = [1,2,3,4];
var data = {};
alert(Array.isArray(nums));
alert(Array.isArray(data));
//true
//false
In this code, Array.isArray() is used to determine which of the two objects is an array.
Note that ECMAScript 3.1 also formalizes the JavaScript 1.6 array extras and JavaScript 1.8 array
reductions discussed earlier in this chapter.
Strings also get a new method, trim() , which removes white space from the beginning and end of text
and returns the result. Here’s an example:
var message = “ Hello world! “;
var newMessage = message.trim();
alert(newMessage); //”Hello world!”
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