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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");

#### <tt>nthCheck(formula)</tt>

First parses, then compiles the formula.

#### <tt>nthCheck.parse(formula)</tt>

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

Example:

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

#### <tt>nthCheck.compile([a, b])</tt>

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