fparser

fparse

A JavaScript Formula Parser

fparse provides a Formula class that parses strings containing mathematical formulas (e.g. x*sin(PI*x/2)) into an evaluationable object. One can then provide values for all unknown variables / functions and evaluate a numeric value from the formula.

For an example application, see http://fparse.alexi.ch/.

Features

Parses a mathematical formula from a string. Known expressions:

• Numbers in the form [-]digits[.digits], e.g. "-133.2945"
• simple operators: '+','-','*','/', expanded in correct order
• parentheses '(', ')' for grouping (e.g. "5*(3+2)")
• all JavaScript Math object functions (e.g. "sin(3.14)")
• all JavaScript Math constants like PI, E
• the use of own functions
• the use of variables
• use it in Web pages and as Node module
• Example:
  -1*(sin(pow(2,x)/(PI*x))*cos(x))

Usage

<!-- Within a web page: Load the fparse library: -->
<script src="fparser.js"></script>

// As node module:
var Formula = require('./fparser');

// 1. Create a Formula object instance by passing a formula string:
var fObj = new Formula('pow(2,x)');

// 2. evaluate the formula, delivering a value object for each unknown entity:
var result = fObj.evaluate({x: 3}); // result = 8

// or deliver multiple value objects to return multiple results:
var results = fObj.evaluate([{x: 2},{x: 4},{x: 8}]); // results = [4,16,256]

// You can also directly evaluate a value if you only need a one-shot result:
var result = Formula.calc('pow(2,x)',{x: 3}); // result = 8
var results = fObj.calc('pow(2,x)',[{x: 2},{x: 4},{x: 8}]); // results = [4,16,256]

// Usage in NodeJS:
var Formula = require('./fparser');
var fObj = new Formula('pow(2,x)');
// .... vice versa

Advanced Usage

Using multiple unknown variables

var fObj = new Formula('a*pow(x,2) + b*x + c');

// Just pass a value object containing a value for each unknown variable:
var result = fObj.evaluate({a:2,b:-1,c:3,x:3}); // result = 18

Using user-defined functions

var fObj = new Formula('sin(inverse(x))');

//Define the function(s) on the Formula object, then use it multiple times:
fObj.inverse = function(value){
    return 1/value;
};
var results = fObj.evaluate({x: 1,x:2,x:3});

// Or pass it in the value object, and OVERRIDE an existing function:
var result = fObj.evaluate({
	x: 2/Math.PI, 
	inverse: function(value){
		return -1*value;
	}
});

If defined in the value object AND on the formula object, the Value object has the precedence