EpsilonJS

EpsilonJS us a JavaScript calculator and an expression parser. The framework allows for parsing mathematical expressions from string or from DOM attributes. It also allows evaluation of mathematical expressions as part of DOM attributes which reference other DOM elements.

How to build EpsilonJS

Clone the repo:

git clone https://github.com/kdinev/EpsilonJS.git

Install the grunt client:

npm install -g grunt-cli bower

Go to the EpsilonJS folder and install dependencies:

cd epsilonjs
npm install
bower install

Build:

grunt default

Description

Parses and evaluates mathematical expressions. The expression is provided to the expression parser as a string.

var expr = "1/(2+8)*2",
    parser = new Epsilon.ExpressionParser(expr);
parser.evaluate(); // Yeilds 0.2 as a number type

Supported operators:

• Addition (+)
• Subtraction (-)
• Multiplication (*)
• Division (/)
• Negative values (-)
• Brackets (())

The epsilon expression parser handles DOM formula references as well. The epsilon expression parser will evaluate all elements containing a data-formula attribute. In order to get the DOM evaluated the Epsilon.epsilon() method needs to be called after loading the DOM. The references need to be like excel cells (e.g. A10, C2) and will be looked-up by id and by data-formula-ref attribute if not found by id. The referenced elements can contain and formula and epsilon will evaluate them according to their data-formula. Circular references are not handled at this point and will result in out of stack space exception.

Example:

<ul>
    <li id="A1">10</li> <!-- <li data-formula-ref="A1">10</li> -->
    <li data-formula="=A1*2"></li>
</ul>
<script type="text/javascript">
    Epsilon.epsilon();
</script>

The result is:

• 10

Epsilon can evaluate only specific DOM elements as well and can be invoked at any point for those elements. If the reference elements contain formulas, then their formulas will be evaluated as part of the requested element's formula but their DOM values will not be changed.

Example:

<ul>
    <li id="A1">10</li> <!-- <li data-formula-ref="A1">10</li> -->
    <li id="A2" data-formula="=A1*2"></li>
    <li id="A3" data-formula="=A2+5"></li>
</ul>
<script type="text/javascript">
    Epsilon.epsilon([document.getElementById("A3")]);
</script>

The result is:

• 10

There is also a jQuery UI epsilon calculator widget provided by https://github.com/kdinev/calculatorjs. This widget was created to test the epsilon expression parser. The calculator widget is dependent on jQuery and jQuery UI. In order to use it:

<div id="calculator"></div>
<script type="text/javascript">
    $(document).ready(function () {
        $("#calculator").calculator();
    });
</script>

The calculator widget is used in a Windows 8.1 store application which you may download and play with here: http://apps.microsoft.com/windows/app/epsilon-calculator/ec41ebdd-00c6-4654-a2a2-b297a0118a87