Description

string-math is a module (function) that computes the [Number] result from the [String] arithmetical formula.
* It does not use eval()
* It uses regular expressions to parse [String] formulas "2+2" into [Number] formulas 2+2. Then it is performed as the common JavaScript arithmetic operation.

``javascript
"2 + 2" //4
"3*(5-2)" //9
" 2.5 * 2.5 / .1" //62.5
"3.5+5(-4-(3/(3+1)-123-.222)-16/412-5/(2)+3.5+2.5(1.5-27))-16" //-225.5
".25e+2*10" //250
`

* Any bugs found? Give me to know on GitHub
If you need to perform arithmetic formulas with the floating point precision (avoid 0.30000000000000004 return values)* or to perform arithmetic formulas with big numbers, check out exact-math package. It implements string-math features as the exactMath.formula method.

Installation

#### with NodeJS / bundlers

npm install string-math

`javascript
var stringMath = require('string-math');

stringMath("--1") //1
stringMath("2/-2") //-1
stringMath("-5-5") //-10
`

#### with Browser

##### 1. Add string-math.js to the HTML file.
`html



`
> Any other dependencies are needed.

##### 2. Use stringMath global Function from string-math.js.
`javascript
var result = stringMath("2+2");
`

##### Browser Support
|Chrome|Firefox|IE|Safari|Opera|
:---:|:---:|:---:|:---:|:---:|
|yes|yes|yes|yes|yes|

Tests

`
> git clone https://github.com/devrafalko/string-math.git
> cd string-math
> npm install
> npm test
> npm test deep //displays error messages
`

Usage

$3

##### expression [String]
* the arithmetical formula
* it can contain:
* [0-9] digits
* 1.5, 0.5 or .5 decimal fractions
* -5, -.4, -5.55 negative values
* 2e-2, .25e+12, -3e-10 exponential notation values
multiplication sign
* / division sign
* + plus sign
* - subtraction sign
* ( and ) parentheses

##### callback [Function] (optional) (synchronous)
* by default, if the callback argument is omitted and the expression is of incorrect type or is invalid, the Error object is thrown. If the callback is defined, the Error object is passed through the callback function, rather than being thrown.
* if the [Function] callback argument is defined, it is called with the following arguments:
* [0] error
It equals null, if the expression is of correct type and is valid math formula.
Otherwise it equals Error object.
* [1] result
It equals null if the expression is of incorrect type or if the math formula is invalid.
Otherwise it equals [Number] result.

Return

If the math formula is of correct type and is valid, it returns the [Number] result. Otherwise it returns null.

Tips

* the arithmetic order of operations is respected:
parentheses first*
then division and multiplication (from left to right)*
then addition and subtraction (from left to right)*
the multiplication sign can be omitted before parentheses; 4(2+1); equals to 4(2+1)
* the following signs combinations are allowed:
2 -2; equals to 2 (-2)*
2 / -2; equals to 2 / (-2)*
+2 + 2; equals to 2 + 2*
2 + +2; equals to 2 + 2*
-2 - -2 equals to -2 + 2*
-2 - +2 equals to -2 - 2*
-2 + -2 equals to -2 - 2*
* the (multi)spaces between values, signs and parentheses are allowed:
* 2 + 2
* 2 + ( -2 - -2)
* 2 + (+2 + +4 / -1)
* -.1 - -5
* 2 + 3e-5
.25e+5 -.25e-5
* the spaces are not allowed between:
* negative sign and value: -2 - - 2
* period and digit in decimal fraction: 5 + . 3
* exponential notation formula: .2 e-5, 2e - 5, 3e +10`