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

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#nth-check

A performant nth-check parser & compiler.

###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().

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

###API

var nthCheck = require("nth-check");

#####nthCheck(formula)

First parses, then compiles the formula.

#####nthCheck.parse(formula)

Parses the expression, throws a SyntaxError if it fails, otherwise returns an array containing two elements.

Example:

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

#####nthCheck.compile([a, b])

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

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 a passed index matches the formula. (Note: The spec starts counting at 1, the returned function at 0).

Example:

var check = nthCheck.compile([2, 3]);

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

License: BSD

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Last updated on 12 Mar 2015

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