performant nth-check parser & compiler
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nth-check Build Status

A performant nth-check parser & compiler.


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.


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

First parses, then compiles the formula.


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


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).


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