#00FFAA + #112233 みたいなのを計算したかっただけ

calcHTMLColor.js

//
// calcHTMLColor("#00FFAA + #112233");
// calcHTMLColor("#00FFAA - #445566");
//
function calcHTMLColor(expression) {
	var replacer = [
		{
			regexp: /\#([0-9A-Fa-f]{2})([0-9A-Fa-f]{2})([0-9A-Fa-f]{2})/g,
			callback: function(str, r, g, b) {
				return "rgb(" + [r,g,b].map(function(n){ return parseInt(n, 16); }).join(",") + ")";
			}
		},
		{
			regexp: /\#([0-9A-Fa-f])([0-9A-Fa-f])([0-9A-Fa-f])/g,
			callback: function(str, r, g, b) {
				return "rgb(" + [r,g,b].map(function(n){ return parseInt(n, 16); }).join(",") + ")";
			}
		},
	];

	replacer.forEach(function(item) {
		expression = expression.replace(item.regexp, item.callback);
	});
	console.log(expression);

	function parseRGB(x) {
		return x.match(/rgb\((.+)\)/)[1].split(",").map(function(n){ return parseInt(n); });
	}
	function toRGB(r,g,b) {
		return "rgb(" + [r,g,b].join(",") + ")";
	}


	var append = expression.match(/(.+)(\+|\-)(.+)/);
	if(append.length == 4) {
		var a = parseRGB(append[1]);
		var b = parseRGB(append[3]);
		a = a.map(function(n, i){
			var x = eval("n" + append[2] + "b[i]");
			if(x>255) x = 255;
			if(x<0) x = 0;
			return x;
		});
		expression = toRGB.apply(this, a);
		console.log(expression);
	}

}