javascript

Chapter 22: The Evolution of JavaScript
The code in this example returns an array containing the result of multiplying each number by two. This
method is helpful when creating arrays whose items correspond to one another.
The last method is forEach() , which simply runs the given function on every item in an array. There is
no return value and is essentially the same as iterating over an array using a for loop. Here’s an example :
var numbers = [1,2,3,4,5,4,3,2,1];
numbers.forEach(function(item, index, array){
//do something here
});
All of these array methods ease the processing of arrays by performing a number of different operations.
The array extras are supported in Chrome, Firefox, Safari 3 and later, and Opera 9.5 and later.
Array and String Generics
A technique introduced earlier in this book used Array.prototype.slice() to create an array out of
the arguments object as shown here:
var args = Array.prototype.slice.call(arguments);
This works because the arguments object is array - like, so it can be passed in as the scope object for the
method. JavaScript 1.6 introduces generic versions of all array and string methods attached to the Array
and String objects. Generic methods expect the first argument to be the object on which to act, and the
other arguments are the same as the instance arguments. For example, the previous code can be
rewritten like this:
var args = Array.slice(arguments);
You can even sort an arguments object without creating an array, like this:
Array.sort(arguments);
Or add a new argument, like this:
Array.push(arguments, “red”);
The same can be done with all string methods. As with the array generic methods, string generic
methods need not be used only on strings. If a different data type is passed in, it is converted into a
string, the operation is performed, and the result is returned as a string, as in this example:
//credit: http://developer.mozilla.org/en/docs/New_in_JavaScript_1.6
var num = 15;
alert(String.replace(num, /5/, “2”)); //”12”
This code produces the string “ 12 ” by converting num into a string and then calling replace() on it.
Array and string generics eliminate the need for explicit data type conversions before working
with values, as well as eliminating the need to access methods on Array.prototype and
String.prototype when used on different data types. Generics are supported in Firefox 1.5 and later.
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