08-27-周三_17-09-29

node_modules/CSSselect/lib/nth-check.js

@@ -0,0 +1,84 @@
+var BaseFuncs = require("./basefunctions.js"),
+    trueFunc  = BaseFuncs.trueFunc,
+    falseFunc = BaseFuncs.falseFunc;
+
+module.exports = function nthCheck(formula){
+	return compile(parse(formula));
+};
+
+module.exports.parse = parse;
+module.exports.compile = compile;
+
+//following http://www.w3.org/TR/css3-selectors/#nth-child-pseudo
+
+//[ ['-'|'+']? INTEGER? {N} [ S* ['-'|'+'] S* INTEGER ]?
+var re_nthElement = /^([+\-]?\d*n)?\s*(?:([+\-]?)\s*(\d+))?$/;
+
+/*
+	parses a nth-check formula, returns an array of two numbers
+*/
+function parse(formula){
+	formula = formula.trim().toLowerCase();
+
+	if(formula === "even"){
+		return [2, 0];
+	} else if(formula === "odd"){
+		return [2, 1];
+	} else {
+		var parsed = formula.match(re_nthElement);
+
+		if(!parsed){
+			throw new SyntaxError("n-th rule couldn't be parsed ('" + formula + "')");
+		}
+
+		var a;
+
+		if(parsed[1]){
+			a = parseInt(parsed[1], 10);
+			if(!a){
+				if(parsed[1].charAt(0) === "-") a = -1;
+				else a = 1;
+			}
+		} else a = 0;
+
+		return [
+			a,
+			parsed[3] ? parseInt((parsed[2] || "") + parsed[3], 10) : 0
+		];
+	}
+}
+
+/*
+	returns a function that checks if an elements index matches the given rule
+	highly optimized to return the fastest solution
+*/
+function compile(parsed){
+	var a = parsed[0],
+	    b = parsed[1] - 1;
+
+	//when b <= 0, a*n won't be possible for any matches when a < 0
+	//besides, the specification says that no element is matched when a and b are 0
+	if(b < 0 && a <= 0) return falseFunc;
+
+	//when a is in the range -1..1, it matches any element (so only b is checked)
+	if(a ===-1) return function(pos){ return pos <= b; };
+	if(a === 0) return function(pos){ return pos === b; };
+	//when b <= 0 and a === 1, they match any element
+	if(a === 1) return b < 0 ? trueFunc : function(pos){ return pos >= b; };
+
+	//when a > 0, modulo can be used to check if there is a match
+	var bMod = b % a;
+	if(bMod < 0) bMod += a;
+
+	if(a > 1){
+		return function(pos){
+			return pos >= b && pos % a === bMod;
+		};
+	}
+
+	a *= -1; //make `a` positive
+
+	return function(pos){
+		return pos <= b && pos % a === bMod;
+	};
+}