Javascript calculator with jQuery

At your attention is a simple tutorial about building a javascript calculator using jQuery. The whole code is explained below and a demo of the calculator is available here: calculator demo.

As I think the markup and the styling are self-explanatory, they would not be shown here explicitly, so let’s start with the code.
First we declare a few variables, half of them pointing to HTML elements.

$calc points to the calculator body, but I am pretty sure it has actually never been used through the code.
$display points at – of course – the calculator display (a div element), while $digits and $operations are sets representing the digits and operations DIVs respectively. The init variable is used by initializing the calculator and resetting the state – of course, it is 0. What operand point to is the first of two operands, taking part in each operation. The operation variable is used to hold the last unexecuted operation, chosen by the user. The afterOperation flag indicates whether the last user’s choice was a digit or an operation. The reset variable, pointing to an anonymous function, resets the display and both operand and operation, used through the code below.

The remaining part of the code is actually a few click handlers – for clicking on a digit or a operation button and two additional – for the decimal point (which I, should admit, wrongly call ‘dot’) and for the change of the sign (+/-). The first function, which comes after the variable declaration and initialization is the digit click handler.

First, as you can see, I exclude the dot and the sign buttons from the elements set, as they actually belong to the digits class, but should be handled a bit differently.
Here the afterOperation flag is used for the first time – there are two options, depending on the flag value – the first one (if (afterOperation == false) {…) is used when we are ‘building’ the value digit by digit and the second one is used to start ‘building’ the value after an operation has been performed. The main difference is in the text() and append() functions – the first one types the clicked digit ($(this).text()) in the display, while the second one simply concatenates the digit to these, already present in the display.
By afterOperation with a value of false, there are analogically two cases – the first one (if ($display.text() == init && $display.text().indexOf(‘.’)<0) {...) checks whether the display has the init value (0) AND whether NO decimal point is available. In this case the text() function is used – that means that the newly chosen digit is written in the display on the init value’s place. The reason to check for the absence of the decimal point, is the following – when we have for example 0 on the display and click the ‘dot’ button for adding a decimal point, the point is concatenated to the zero. However, the expression “0.” == 0 evaluates to true and so the text() function would be invoked, while we need to append digits after the decimal point – so the $display.text().indexOf(‘.’)<0 statement has been added. So in the case “0.” we have true for the first statement $display.text() == init and false for the second one, thus eventually having true AND false, which evaluates to false, making the code appending digits after the dot instead of not resetting the display with the text() function.
Let’s now have a look at the operation handler.

First, we make two additional local variables – currOperation for the current operation and currOperand for the current operand. Then we simply check if the Clear button is pressed – if so, we call the reset() function.
If not, however, we go on with the math.
First, we check if there is already an operation set AND whether the flag afterOperation has a value of false, which means that no operation button has been clicked just before the event, being handled at the moment. If both the upper conditions are satisfied, a switch statement (for the operation, not currOperation) takes care for doing the math. Please note that if we have typed a value (e.g. 5) for example, than chosen ‘+’ operation, type a value again and chose a ‘-‘ operation, the operation variable would point to the last unhandled one – that means the plus operation, so it would be caught and executed by the switch statement. So, at the moment of clicking on the minus sign, the plus operation would be executed.
The expression if (currOperation != ‘=’) {operation = currOperation;} takes care of assigning the current and still not executed operation (the ‘minus’ from the example above) to the operation variable. The operation behind the equal sign is, of course, not to be remembered anywhere – by clicking on the equal sign, we execute the last available operation and reset the operation and the afterOperation flag.
However, no matter how many times we have clicked on an operation button (different from “CE” and “=”),

statements would be executed – operand should point to the value, currently available on the display (that is – most likely – the result of the past operation) and afterOperation should be true.
The last two handlers are for the decimal point and the switch sign.

The ‘dot’ click handler appends a single dot to the digits available in the display if afterOperation flag is false or writes “0.” string in the display in case an operation button has been just clicked on.
The ‘sign’ click handler switched the sign only if the afterOperation flag is set to false.

I really hope the article has been useful and adequately responding to your needs.

RSS file update system with ajax and jquery

After the article about parsing xml/rss data with jquery’s ajax functions, I would now show you how the editing system for the Useful links repository page has been made.
What it actually does is editing/deleting and creating of rss files and respectively the items in them without a single refresh. The most relevant part of the client-side and the whole part of the server-side would be shown.

A demo of the system is here to be found
Please note that no data would be send to the server-side .php file – the ajax function doing this is commented and will not execute. That’s why when reloading the page you are going to see only the currently available categories and their corresponding items – changes made by you would not affect the files and its contents. Please also note that editing of a category or item, newly created by you would also be not possible, because of the same reason – editing is based on existing files and since the demo page actually does not create or alter anything in the categories folder on the server, it would not work as expected when for example trying to edit item in the category you have just added one to.

The files, used by the system:

index.php – the admin start page, containing HTML and a bit of PHP to list all the currently existing category files (each category file is a RSS file, all available under the Useful Links Repository page)
adminProcessesController.js – the client-side code which reads existing files and sends requests about file manipulation to the server-side page below (available from the link above)
adminProcesses.php – the server-side code, which handles the ajax requests, done by the client-side page above
– RSSDocument.php – a file, containing the ifactnet_RSSDocument class, extending the DOMDocument PHP class.
– ifactnet_util.php – a file, containing some little functions (e.g. obtaining files in a folder by given extension, returning the absolute file name (without the extension) and so on…)
– style.css

The entry point – index.php – contains actually a few lines of code, whose main goal is to create the menu, used for the editing. The menu has the following structure:

  • Create new category
  • [Category 1]
    • Create new item
    • [Item 1 in Category 1]
    • [Item 2 in Category 1]
  • [Category 2]
    • Create new item
    • [Item 1 in Category 2]


Clicking on each item or category link gives a possibility to edit it or delete it, creating of items and categories is also done by clicking on the corresponding “Create” option. Let’s now have a look at the more interesting files:


The current file is the most important, and so the biggest from the set above and would be unfortunately not possible to explain it in details, but I will try to cover the most important moments.
AJAX is used in two functions, declared at the very beginning of the file – the first one for reading an item or channel properties from a .xml file and the second one for sending requests to the php page:

loadSelected variable (that is unnamed (anonymous) function, assigned to a variable):
The arguments are pretty much self-explanatory – indexSelected is the index of the selected item (obtained by clicking on its title – that a bit latter) and the second one is the path to the xml files. As already explained in a previous article about ajax – the path should be relative to the root directory of your server – for example, the paths, used in css and javascript files are relative to the .html file, where they are included. A path for ajax call to a file under ‘’ should be “/lib/news.rss”, no matter where the javascript file, making the ajax call, actually is.
The ajax call parameters, used in the current function are to be found on the ajax methods documentation page in jquery’s website. There is, however, an important thing to notice – when returning any data, ‘fetched’ from the call, use async: false, like in the example above.
The success callback function returns the item node or an array of three of the channel’s node children – title, description and link. Its argument is the obtained xml (in this case – the whole xml file).

callServerSide variable (again unnamed (anonymous) function, assigned to a variable):
The function uses POST method to send the properties argument to the server side page, the path to which is assigned to path argument.
data property of the ajax function should point to the data, which we are about to send. As you would see later – the data is a regular POST string with the form key1=”value1″&key2=”value2″. dataType is the type of data, expected as answer from the server-side script – in this case it is a plain text, as what the current server-side script returns is either “true” or “false”. The data, returned from the server is passed to the first argument of the success callback function – in our case that be returnedData. Of course, you can name the argument differently.

What the file does further:
It ‘splits’ the different links from the menu by purpose – item editing/deleting, item creating, or category editing/deleting and creating, assigning different anchor sets (depending on the anchors’ classes) to different variables (shown below).
Each set of anchors (for item editing/deleting or item creating, etc…) is handled a little differently on click. Basically, the handling procedures could be categorized as Creating and Editing/Deleting ones.
The creating procedures are a bit tricky, as the newly created item/category titles should be prepended to the menu on the go – as you remember, the menu is created in the index.php with a php code. However, as the aim is to accomplish all the tasks without reloading, the newly created items should be created in both the corresponding file (this is done by the php script) AND in the menu itself. Analogically – newly created categories demand creating of both the category file and the category ‘entry’ in the menu.
Editing procedures edit the content of the item/category in both the files and the menu entries.
When each of the procedures is started (by clicking on the corresponding menu entry(anchor)), a form is shown – with blank fields for creating procedure and populated ones for editing. Both are explained few lines below.
The form submission is the part, where the server-side script is called and the editing/deleting and creating processes are actually handled.

Let’s already come back to the code and especially the different kinds of menu entries:

What is omitted is the initialization of another variables, needed for the current implementation of the admin system. As the aim of the article is only pointing out the sole idea behind the ajax calls and the server side script, executed on their request, these are not included in the code. The dollar sign ($) at the beginning of each variable only denotes that the variable holds/points to jQuery object/set of objects.
The variables above are used as follows:

An important part here is the use of “live” – it binds the click event not only to the anchors, already created, but also to these, which are appended to the menu on the go – when an item or category is newly created.

What was omitted here (but shown a couple of rows below) is the call of the loadSelected() function. By item/category editing procedure, a form is created on the go and eventually appended to the main div in index.php. Its fields are populated with the data, returned from loadSelected() and a Delete button is added as well.
By creation process, the corresponding forms are shown with blank fields (these forms are already present in the index.php. They are, of course, hidden, until a creation link is clicked on).
Have a look at the code, handling item editing procedure, but have in mind that there are few functions and variables used, whose implementation and declaration are not shown. However, the functions are self-explanatory and all the variables represent different html elements. The only thing which could be of interest here, is the hideTheseNodeValues array – it contains all the item values, which are not to be edited – currently only the pudDate, actually.

The last parts of the javascript file are the forms submit handlers and the delete actions, where the callServerSide function is called.

The serialize() function is the one, creating the POST string – as mentioned at the beginning of the article – it holds key-value pairs, where the keys are the form input names and values are the strings, typed in the corresponding input fields.
The creation processes are pretty much the same, as these shown above, except that they handle the additional appending of items to the menu – that is: [Item N in category M] menu entry for an item or
-[New category name]
– Create new item in [New category name]
menu entries for a whole new category.
The issue: items are created in category files by the php script, categories are created as new files by the same php file, but all that results in different menu structure, which should be handled by the javascript, if no reloading is needed. The alternative of the on-the-go appending of menu entries is a simple refresh of the page – then index.php would list all the existing files and its contents. (I have written about that in the very beginning of the article). However, this refresh would make the whole ajax processing useless – each form action could call the adminProcesses.php file directly, which would handle the request accordingly and eventually reopen the index.php for further item/category processing from user’s side.

The last part of the file:

handles the deleting of both item and category and removing its menu entries respectively. callServerSide function is called again, only with different parameters, of course.


Finally, the complete server-side code:

The file uses couple of functions from the ifactnet_util.php, mentioned at the beginning of the article, which, I hope, are self-explanatory. The ifactnet_RSSDocument class is going to be included in another post for free use.

What adminProcessing.php actually does is to either edit, delete or create an item or a category, using a controlling variable – $action. As a response for each task, it simply echoes true on success, or false on failure, thus ‘sending’ it to the AJAX call (callServerSide()), which returns it to a certain variable (already in the javascript file – adminProcessesController.js). According to the answer, returned from the server side, either an error or success message message is shown.
The adminProcessing.php uses the POST request, sent from the AJAX call in its $_POST variable – take for example the following POST string – item=item1&title=title1, which would result in a $_POST array with two pairs key=>value – $_POST[‘item’] would give ‘item1’ and $_POST[‘title’] would give title1.


What AJAX enables us to do is to send either GET or POST requests to be (PUT and DELETE are available as well – refer to the ajax() manual in the jQuery website) processed by the server (in our case the server processing is actualy the adminProcesses.php file) without reloading the page.
Data sent to the server via POST method for example is available in the php $_POST array. The data is processed by the server and when needed is ‘returned’ to the same ajax call with a simple echo statement. When expecting data from the server-side, it is good to set the dataType property of the ajax function to the data type you are waiting – e.g. text, json or xml. However, not doing so would simply result in the so called “intelligent guess” – the jQuery would try to guess what type the received data is.
I hope that the article was of use for you, though its length and the fairly big amount of code not shown here, but taking part in the whole script.