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