decimal-eval

A tiny, safe, fast JavaScript library for decimal arithmetic expressions.


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Features

- :v: Automatically deal with the JavaScript decimal precision problem by bignumber.js, and supports big number
- :rocket: Fast and tiny, only 28.7 KB minified and 11.2 KB gzipped (pure only 10.5 KB minified and 3.3 KB gzipped without bignumber.js)
- :writing_hand: Easy to extend custom operator
- :vulcan_salute: Supports expression scope variables

Get Started

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``

use npm

npm i -S decimal-eval

or use yarn

yarn add decimal-eval
`

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Supports the four arithmetic operations (+, -, *, /),
and automatically deal with JavaScript decimal precision by bignumber.js, and supports big number.

`js
import {evaluate} from 'decimal-eval';

evaluate('0.1 + 0.2') // '0.3'
evaluate('100 * (0.08 - 0.01)'); // '7'
evaluate('9007199254740992 + 1'); // '9007199254740993'
evaluate('1 + abc', { abc: 2 }); // '3'
`

In addition to the above operators, it also supports custom operator expansion,
and supports unary operators and binary operators.
The operator precedence according to: MDN operator precedence.

`js
import {evaluate, Parser} from 'decimal-eval';

// create binary operator add, the precedence is 13
const addOp = Parser.createBinaryOperator('add', 13, (left, right) => {
return String(Number(left) + Number(left));
});

// create unary operator sin, the precedence is 16
const sinOp = Parser.createUnaryOperator('sin', 16, (value) => {
return String(Math.sin(value));
});

// install custom operators
Parser.useOperator(addOp);
Parser.useOperator(sinOp);

// same as: 1 + Math.sin(-2)
evaluate('1 add sin -2') // '0.09070257317431829'
`




API

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Parse the arithmetic expression and then calculate the result. The name of scope has the following restrictions:
- muse be start with a-z or A-Z
- only includes a-z、A-Z、0-9 and _

`js
import {evaluate} from 'decimal-eval';

evaluate('1 + 2'); // '3'
evaluate('1 + abc', { abc: 2 }); // '3'
`

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#### new Parser(expression: string).parse(): Node | null
Parse arithmetic expressions.

`js
import {Parser} from 'decimal-eval';

const node = new Parser('1 + 2').parse();
`

#### new Parser(expression: string).compile(): (scope: Record) => string
Compile and cache the arithmetic expression.

`js
import {Parser} from 'decimal-eval';

const evaluate = new Parser('1 + abc').compile();
evaluate({ abc: 2 }); // '3'
evaluate({ abc: 9 }); // '10'
evaluate({ def: 1 }); // throw error, the scope name abc is not initialized
`

#### Parser.createBinaryOperator(value: string, precedence: number, calc: (left: string, right: string) => string): Operator
Create a binary operator.

#### Parser.createUnaryOperator(value: string, precedence: number, calc: (value: string) => string): Operator
Create a unary operator.

#### Parser.useOperator(operator: Operator): void
Install an operator which created by the Parser.createBinaryOperator() or Parser.createUnaryOperator() method.

#### Parser.useAdapter(adapter)
Set custom calculation adapter methods for four arithmetic (+, -, *, /).
bignumber.js is used by default.

`js
Parser.useAdapter({
'+': (left, right) => String(Number(left) + Number(right)),
'-': (left, right) => String(Number(left) - Number(right)),
'': (left, right) => String(Number(left) Number(right)),
'/': (left, right) => String(Number(left) / Number(right))
})
`




Advanced

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When using a custom method to deal with the decimal precision problem, you can use a pure package, which can reduce the size by about 60%.
It doesn't include bignumber.js.

`js
import {evaluate, Parser} from 'decimal-eval/dist/pure';

// set custom calculation adapter
// Parser.useAdapter(adapter);

// Does not deal with precision by default
evaluate('0.1 + 0.2'); // '0.30000000000000004'

// not supports big number by default
evaluate('9007199254740992 + 1'); // '9007199254740992'
`

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Useful for deal JavaScript decimal precision problem without having to install bignumber.js again.

`js
import {BigNumber} from 'decimal-eval';
const val = new BigNumber(0.1).plus(0.2);
console.log(String(val)); // '0.3'
`

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The operator precedence according to: MDN operator precedence.

| operator | precedence |
| -------- | ---------- |
| ... + ... | 13 |
| ... - ... | 13 |
| ... * ... | 14 |
| ... / ... | 14 |
| + ... | 16 |
| - ...` | 16 |