- The $A() function converts the single argument it receives - into an Array object. -
-- This function, combined with the extensions for the Array class, - makes it easier to convert or copy any enumerable list into an - Array object. One suggested use is to convert DOM - NodeLists into regular arrays, which can be traversed - more efficiently. See example below. -
- -- The $H() function converts - objects into enumerable Hash objects that - resemble associative arrays. -
-- We are all familiar with for-loops. You know, create yourself an array, populate it with - elements of the same kind, create a loop control structure (for, foreach, while, repeat, etc,) - access each element sequentially, by its numeric index, and do something with the element. -
-- When you come to think about it, almost every time you have an array in your code it - means that you'll be using that array in a loop sooner or later. Wouldn't it be nice - if the array objects had more functionality to deal with these iterations? Yes, it would, - and many programming languages provide such functionality in their arrays or equivalent - structures (like collections and lists.) -
- -- Well, it turns out that prototype.js gives us the Enumerable - object, which implements a plethora of tricks for us to use when dealing with iterable data. - The prototype.js library goes one step further and extends the - Array class with all the methods of Enumerable. -
- - -- In standard javascript, if you wanted to sequentially display the elements of an array, - you could very well write something like this. -
-- With our new best friend, prototype.js, we can rewrite this loop like this. -
- -- You are probably thinking "big freaking deal...just a weird syntax for the same old thing." - Well, in the above example, yes, there's nothing too earth shattering going on. After all, - there's not much to be changed in such a drop-dead-simple example. But - keep reading, nonetheless. -
-- Before we move on. Do you see this function that is being passed as an argument - to the each method? Let's start referring to it as an - iterator function. -
- -- Like we mentioned above, it's very common for all the elements in your array to be of - the same kind, with the same properties and methods. Let's see how we can take advantage - of iterator functions with our new souped-up arrays. -
-- Finding an element according to a criteria. -
-
- Now let's kick it up another notch. See how we can filter out - items in arrays, then retrieve just a desired member from each - element. -
-
- This <a href="http://othersite.com/page.html">text</a> has
- a <a href="#localAnchor">lot</a> of
- <a href="#otherAnchor">links</a>. Some are
- <a href="http://wherever.com/page.html">external</a>
- and some are <a href="#someAnchor">local</a>
-
- It takes just a little bit of practice to get completely addicted to this syntax. - Next we will go through the available functions with the following example. -
-I used to find myself writing a lot of for loops. Although,
-Prototype does not by any means eliminate the need to do for-loops,
-it does give you access to what I consider to be a cleaner, easier to read method in each.
-
-The each function allows us to iterate over these objects Ruby style. -
-The each function takes one argument, an iterator function. -This iterator is invoked once for every item in the array, and that item -along with the optional index is passed to the iterator. So if -we also needed the index we could do something like the code below. -
- -Hashes can be created by wrapping an Object (associative array) in -$H() and can have their key/value pairs exposed.
- --We can also directly access the keys and values of a Hash without iterating over it. -
-The collect function allows you to iterate over an Array and return the -results as a new array. Each item returned as a result of the iteration will be -pushed onto the end of the new array.
-You can even join on the end of the block.
-The include function allows you to check if a value is included in an array -and returns true or false depending on if a match was made. Assuming I put -up a form asking the user to name some artist in my iTunes playlist, -we could do something like the code below. Prime candidate for some conditional madness. -
-The inject function is good for getting a collective sum from an array of -values. For instance, to add up all the numbers. -
-The first argument to inject is just an initial value that -would be added to the sum, so if we added 1 instead of 0, the output would be 162.
- --When given an Array, the findAll function will return an array of -items for which the iterator evaluated to true. Basically, it allows you to -build a new array of values based on some search criteria. -If we wanted to find all products whose type was “E-Commerce” -we could do something like the code below. -
-Note that even if only one match is made, just as in this case, -the result is still returned as an array. In that case, -ecom.company would return undefined.
- -Unlike the findAll function, the detect function will only -return the first item for which the expression inside -the iterator is true. So, if we wanted to find the first number that -was greater than 5 we’d do something like the code below. -
-Even though, there are other numbers above 5 in our array, detect -only gives us the first match back.
- -The invoke function allows us to pass a method as a string and -have that method invoked. For instance, if we wanted to sort -our array of artists we’d do something like this:
- -Why not just use F.Artists.sort? Well, for the example above -we could do just that, but here is where invoke shines.
- -So we invoked sort for each sub-array. Note that the code below will not work.
- -The reason this will not work is because it is taking each item -in that array and trying to apply sort to it, thus if we wrote it outright, -it would look something like this:
- -We could however do something like this:
- --Now, what about passing arguments to the invoke function? -The first argument passed to invoke is the method to be invoked, -and any other arguments beyond that will be passed as arguments to the invoked method.
- -