@yaeda/calculator

A simple JavaScript library for evaluating mathematical expressions.

Features

• Supports basic arithmetic operations (+, -, *, /)
• Supports parentheses ((, )), exponentiation (^), and square root (sqrt)
• Supports 見せ算 (@)
  • same precedence as multiplication and division, and left-associative
• Allows omission of multiplication sign between number and parentheses
• Allows changing the number of decimal places with an option

Installation

You can install the library via npm:

npm install @yaeda/calculator

Usage

First, import the calc function from the library:

import { calc } from "@yaeda/calculator";

Example

Here are some examples of how to use the calc function:

import { calc } from "@yaeda/calculator";

calc("0.1 + 0.2"); // 0.3
calc("1 * 2 + 3 / 4 -  5"); // -2.25
calc("2 * 2 ^ 2"); // 8
calc("2(3+4)"); // 14

// round to specified decimal places
calc("3.14159265359", { digits: 2 }); // 3.14
calc("1 / 3", { digits: 3 }); // 0.333

// invalid expression
calc("invalid expression"); // null

For more examples, please refer to the test directory.

API

calc

/**
 * Evaluates a mathematical expression and returns the result rounded to a specified number of decimal places.
 *
 * @param {string} expr - The mathematical expression to evaluate.
 * @param {Option} [option] - Optional settings.
 * @param {number} [option.digits=10] - The number of decimal places to round the result to. Defaults to 10 if not provided.
 * @returns {number|null} The evaluated result rounded to the specified number of decimal places, or null if an error occurs.
 */
export const calc: (expr: string, option?: Option) => number | null;

Option

/**
 * @typedef {Object} Option
 * @property {number} digits - The number of decimal places to round the result to.
 */
export type Option = {
  digits: number;
};

Expression Syntax

The syntax for the mathematical expressions is defined using Extended Backus-Naur Form (EBNF):

<expression> ::= <term> | <expression> ("+" | "-") <term>
<term>       ::= <factor> | <term> ("*" | "/" | "@") <factor>
<factor>     ::= <base> | <base> "^" <factor>
<base>       ::= <number> | ("+" | "-" | "sqrt") <base> | "(" <expression> ")" | <number> "(" <expression> ")"
<number>     ::= \d+(\.\d+)?

References

This library is based on and inspired by the following projects:

• microsoft/ts-parsec
• Ran350/misezan