parse.js
1.15 KB
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"use strict";
// Following http://www.w3.org/TR/css3-selectors/#nth-child-pseudo
Object.defineProperty(exports, "__esModule", { value: true });
exports.parse = void 0;
// [ ['-'|'+']? INTEGER? {N} [ S* ['-'|'+'] S* INTEGER ]?
var RE_NTH_ELEMENT = /^([+-]?\d*n)?\s*(?:([+-]?)\s*(\d+))?$/;
/**
* Parses an expression.
*
* @throws An `Error` if parsing fails.
* @returns An array containing the integer step size and the integer offset of the nth rule.
* @example nthCheck.parse("2n+3"); // returns [2, 3]
*/
function parse(formula) {
formula = formula.trim().toLowerCase();
if (formula === "even") {
return [2, 0];
}
else if (formula === "odd") {
return [2, 1];
}
var parsed = formula.match(RE_NTH_ELEMENT);
if (!parsed) {
throw new Error("n-th rule couldn't be parsed ('" + formula + "')");
}
var a;
if (parsed[1]) {
a = parseInt(parsed[1], 10);
if (isNaN(a)) {
a = parsed[1].startsWith("-") ? -1 : 1;
}
}
else
a = 0;
var b = (parsed[2] === "-" ? -1 : 1) *
(parsed[3] ? parseInt(parsed[3], 10) : 0);
return [a, b];
}
exports.parse = parse;