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nth-check/README.md

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1# nth-check [![Build Status](https://travis-ci.org/fb55/nth-check.svg)](https://travis-ci.org/fb55/nth-check)
2
3Parses and compiles CSS nth-checks to highly optimized functions.
4
5### About
6
7This module can be used to parse & compile nth-checks, as they are found in CSS 3's `nth-child()` and `nth-last-of-type()`.
8
9`nth-check` focusses on speed, providing optimized functions for different kinds of nth-child formulas, while still following the [spec](http://www.w3.org/TR/css3-selectors/#nth-child-pseudo).
10
11### API
12
13```js
14import nthCheck, { parse, compile } from "nth-check";
15```
16
17##### `nthCheck(formula)`
18
19Parses and compiles a formula to a highly optimized function. Combination of `parse` and `compile`.
20
21If the formula doesn't match any elements, it returns [`boolbase`](https://github.com/fb55/boolbase)'s `falseFunc`. Otherwise, a function accepting an _index_ is returned, which returns whether or not the passed _index_ matches the formula.
22
23**Note**: The nth-rule starts counting at `1`, the returned function at `0`.
24
25**Example:**
26
27```js
28const check = nthCheck("2n+3");
29
30check(0); // `false`
31check(1); // `false`
32check(2); // `true`
33check(3); // `false`
34check(4); // `true`
35check(5); // `false`
36check(6); // `true`
37```
38
39##### `parse(formula)`
40
41Parses 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.
42
43**Example:**
44
45```js
46parse("2n+3"); // [2, 3]
47```
48
49##### `compile([a, b])`
50
51Takes an array with two elements (as returned by `.parse`) and returns a highly optimized function.
52
53**Example:**
54
55```js
56const check = compile([2, 3]);
57
58check(0); // `false`
59check(1); // `false`
60check(2); // `true`
61check(3); // `false`
62check(4); // `true`
63check(5); // `false`
64check(6); // `true`
65```
66
67---
68
69License: BSD-2-Clause
70
71## Security contact information
72
73To report a security vulnerability, please use the [Tidelift security contact](https://tidelift.com/security).
74Tidelift will coordinate the fix and disclosure.
75
76## `nth-check` for enterprise
77
78Available as part of the Tidelift Subscription
79
80The maintainers of `nth-check` and thousands of other packages are working with Tidelift to deliver commercial support and maintenance for the open source dependencies you use to build your applications. Save time, reduce risk, and improve code health, while paying the maintainers of the exact dependencies you use. [Learn more.](https://tidelift.com/subscription/pkg/npm-nth-check?utm_source=npm-nth-check&utm_medium=referral&utm_campaign=enterprise&utm_term=repo)

1	`# nth-check [![Build Status](https://travis-ci.org/fb55/nth-check.svg)](https://travis-ci.org/fb55/nth-check)`
2
3	`Parses and compiles CSS nth-checks to highly optimized functions.`
4
5	`### About`
6
7	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()`.
8
9	`nth-check` focusses on speed, providing optimized functions for different kinds of nth-child formulas, while still following the [spec](http://www.w3.org/TR/css3-selectors/#nth-child-pseudo).
10
11	`### API`
12
13	```js
14	`import nthCheck, { parse, compile } from "nth-check";`
15	```
16
17	##### `nthCheck(formula)`
18
19	Parses and compiles a formula to a highly optimized function. Combination of `parse` and `compile`.
20
21	If the formula doesn't match any elements, it returns [`boolbase`](https://github.com/fb55/boolbase)'s `falseFunc`. Otherwise, a function accepting an _index_ is returned, which returns whether or not the passed _index_ matches the formula.
22
23	Note: The nth-rule starts counting at `1`, the returned function at `0`.
24
25	`Example:`
26
27	```js
28	`const check = nthCheck("2n+3");`
29
30	check(0); // `false`
31	check(1); // `false`
32	check(2); // `true`
33	check(3); // `false`
34	check(4); // `true`
35	check(5); // `false`
36	check(6); // `true`
37	```
38
39	##### `parse(formula)`
40
41	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.
42
43	`Example:`
44
45	```js
46	`parse("2n+3"); // [2, 3]`
47	```
48
49	##### `compile([a, b])`
50
51	Takes an array with two elements (as returned by `.parse`) and returns a highly optimized function.
52
53	`Example:`
54
55	```js
56	`const check = compile([2, 3]);`
57
58	check(0); // `false`
59	check(1); // `false`
60	check(2); // `true`
61	check(3); // `false`
62	check(4); // `true`
63	check(5); // `false`
64	check(6); // `true`
65	```
66
67	`---`
68
69	`License: BSD-2-Clause`
70
71	`## Security contact information`
72
73	`To report a security vulnerability, please use the [Tidelift security contact](https://tidelift.com/security).`
74	`Tidelift will coordinate the fix and disclosure.`
75
76	## `nth-check` for enterprise
77
78	`Available as part of the Tidelift Subscription`
79
80	The maintainers of `nth-check` and thousands of other packages are working with Tidelift to deliver commercial support and maintenance for the open source dependencies you use to build your applications. Save time, reduce risk, and improve code health, while paying the maintainers of the exact dependencies you use. [Learn more.](https://tidelift.com/subscription/pkg/npm-nth-check?utm_source=npm-nth-check&utm_medium=referral&utm_campaign=enterprise&utm_term=repo)