41 lines
839 B
JavaScript
41 lines
839 B
JavaScript
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module.exports = parse;
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//following http://www.w3.org/TR/css3-selectors/#nth-child-pseudo
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//[ ['-'|'+']? INTEGER? {N} [ S* ['-'|'+'] S* INTEGER ]?
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var re_nthElement = /^([+\-]?\d*n)?\s*(?:([+\-]?)\s*(\d+))?$/;
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/*
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parses a nth-check formula, returns an array of two numbers
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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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} else if(formula === "odd"){
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return [2, 1];
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} else {
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var parsed = formula.match(re_nthElement);
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if(!parsed){
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throw new SyntaxError("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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if(parsed[1].charAt(0) === "-") a = -1;
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else a = 1;
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}
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} else a = 0;
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return [
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a,
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parsed[3] ? parseInt((parsed[2] || "") + parsed[3], 10) : 0
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];
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}
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}
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