CSS Calc

Implemented from : https://drafts.csswg.org/css-values-4/ on 2023-02-17

Usage

Add CSS calc to your project:

npm install @csstools/css-calc @csstools/css-parser-algorithms @csstools/css-tokenizer --save-dev

With string values :

import { calc } from '@csstools/css-calc';

// '20'
console.log(calc('calc(10 * 2)'));

With component values :

import { stringify, tokenizer } from '@csstools/css-tokenizer';
import { parseCommaSeparatedListOfComponentValues } from '@csstools/css-parser-algorithms';
import { calcFromComponentValues } from '@csstools/css-calc';

const t = tokenizer({
    css: 'calc(10 * 2)',
});

const tokens = [];

{
    while (!t.endOfFile()) {
        tokens.push(t.nextToken());
    }

    tokens.push(t.nextToken()); // EOF-token
}

const result = parseCommaSeparatedListOfComponentValues(tokens, {});

// filter or mutate the component values

const calcResult = calcFromComponentValues(result, { precision: 5, toCanonicalUnits: true });

// filter or mutate the component values even further

const calcResultStr = calcResult.map((componentValues) => {
    return componentValues.map((x) => stringify(...x.tokens())).join('');
}).join(',');

// '20'
console.log(calcResultStr);

Options

precision :

The precision option is a number of decimals. The default precision is fairly high. It aims to be high enough to make rounding unnoticeable in the browser.

Values that serialize in scientific notation are left untouched.

You can set it to a lower number to suit your needs.

import { calc } from '@csstools/css-calc';

// '0.3'
console.log(calc('calc(1 / 3)', { precision: 1 }));
// '0.33'
console.log(calc('calc(1 / 3)', { precision: 2 }));
// '1.0000000000000001e-20'
console.log(calc('calc(1e-10 * 1e-10)'));

globals :

Pass global values as a map of key value pairs.

Example : Relative color syntax (lch(from pink calc(l / 2) c h)) exposes color channel information as ident tokens. By passing globals for l, c and h it is possible to solve nested calc()'s.

import { calc } from '@csstools/css-calc';

const globals = new Map([
    ['a', '10px'],
    ['b', '2rem'],
]);

// '20px'
console.log(calc('calc(a * 2)', { globals: globals }));
// '6rem'
console.log(calc('calc(b * 3)', { globals: globals }));

toCanonicalUnits :

By default this package will try to preserve units. The heuristic to do this is very simplistic. We take the first unit we encounter and try to convert other dimensions to that unit.

This better matches what users expect from a CSS dev tool.

If you want to have outputs that are closes to CSS serialized values you can pass toCanonicalUnits: true.

import { calc } from '@csstools/css-calc';

// '20hz'
console.log(calc('calc(0.01khz + 10hz)', { toCanonicalUnits: true }));

// '20hz'
console.log(calc('calc(10hz + 0.01khz)', { toCanonicalUnits: true }));

// '0.02khz' !!!
console.log(calc('calc(0.01khz + 10hz)', { toCanonicalUnits: false }));

// '20hz'
console.log(calc('calc(10hz + 0.01khz)', { toCanonicalUnits: false }));