# 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)-12*3-.2*22)-16/4*12-5/(2)+3.5+2.5*(1.5-2*7))-16" //-225.5 ".25e+2*10" //250 ``` * Any bugs found? Give me to know on [GitHub](https://github.com/devrafalko/string-math) * 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`**](https://www.npmjs.com/package/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 ### `stringMath(expression[,callback])` ##### `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`