nth-check

What is nth-check?

The nth-check package is a utility for parsing and evaluating CSS nth-expressions, such as those used in :nth-child or :nth-of-type pseudo-classes. It allows developers to determine if an element is the nth child of its parent based on the given nth-expression.

What are nth-check's main functionalities?

Parsing nth-expressions

This feature allows for parsing a CSS nth-expression and returns a function that can be used to check if a given index matches the nth-expression.

const nthCheck = require('nth-check');
const check = nthCheck('2n+3');
console.log(check(5)); // true

Evaluating nth-expressions

This feature evaluates whether a given index (like the position of an element among its siblings) matches the nth-expression, such as 'odd' or 'even'.

const nthCheck = require('nth-check');
const check = nthCheck('odd');
console.log(check(1)); // true
console.log(check(2)); // false

Other packages similar to nth-check

css-what

css-what is a package for parsing CSS selectors. It provides functionality to parse complex selectors into understandable parts but does not directly evaluate nth-expressions like nth-check.

sizzle

Sizzle is a pure-JavaScript CSS selector engine designed to be easily dropped in to a host library. It is capable of complex CSS queries, including nth-expressions, but it is more comprehensive and not as focused as nth-check.

README

nth-check

Parses and compiles CSS nth-checks to highly optimized functions.

About

This module can be used to parse & compile nth-checks, as they are found in CSS 3's nth-child() and nth-last-of-type(). It can be used to check if a given index matches a given nth-rule, or to generate a sequence of indices matching a given nth-rule.

nth-check focusses on speed, providing optimized functions for different kinds of nth-child formulas, while still following the spec.

API

import nthCheck, { parse, compile } from "nth-check";

nthCheck(formula)

Parses and compiles a formula to a highly optimized function. Combination of parse and compile.

If the formula doesn't match any elements, it returns boolbase's falseFunc. Otherwise, a function accepting an index is returned, which returns whether or not the passed index matches the formula.

Note: The nth-rule starts counting at 1, the returned function at 0.

Example:

const check = nthCheck("2n+3");

check(0); // `false`
check(1); // `false`
check(2); // `true`
check(3); // `false`
check(4); // `true`
check(5); // `false`
check(6); // `true`

parse(formula)

Parses the expression, throws an Error if it fails. Otherwise, returns an array containing the integer step size and the integer offset of the nth rule.

Example:

parse("2n+3"); // [2, 3]

compile([a, b])

Takes an array with two elements (as returned by .parse) and returns a highly optimized function.

Example:

const check = compile([2, 3]);

check(0); // `false`
check(1); // `false`
check(2); // `true`
check(3); // `false`
check(4); // `true`
check(5); // `false`
check(6); // `true`

generate([a, b])

Returns a function that produces a monotonously increasing sequence of indices.

If the sequence has an end, the returned function will return null after the last index in the sequence.

Example: An always increasing sequence

const gen = nthCheck.generate([2, 3]);

gen(); // `1`
gen(); // `3`
gen(); // `5`
gen(); // `8`
gen(); // `11`

Example: With an end value

const gen = nthCheck.generate([-2, 5]);

gen(); // 0
gen(); // 2
gen(); // 4
gen(); // null

sequence(formula)

Parses and compiles a formula to a generator that produces a sequence of indices. Combination of parse and generate.

Example: An always increasing sequence

const gen = nthCheck.sequence("2n+3");

gen(); // `1`
gen(); // `3`
gen(); // `5`
gen(); // `8`
gen(); // `11`

Example: With an end value

const gen = nthCheck.sequence("-2n+5");

gen(); // 0
gen(); // 2
gen(); // 4
gen(); // null

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License: BSD-2-Clause

Security contact information

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