tiny mustache-like templating engine in 2.6kb/108 loc

example.js

var template = "{?condition}Condition exists! {condition}{/condition}\n\n" +
  "{^whereami}I am not here!{/whereami}\n\n" +
  "{#list}{name} is {age} years old! {?old}They are *old*!{/old}{!old}They are not old!{/old}\n{/list}";

console.log(stache(template, {
  condition: "Hello world!",
  list: [
	  {name: "Charles", age: "25"},
	  {name: "Bob", age: "42", old: true},
	  {name: "Samantha", age: "32"},
  ]
}));

stache.js

var stache = (function (template, data) {
	function get(scope, key) {
		for(var i = scope.length - 1; i >= 0; i --)
			if (scope[i][key])
				return scope[i][key];

		return null;
	}

	function accept (tokens, types) {
		var token;

		if (types.indexOf((token = (tokens.length > 0 ? tokens.shift() : ["eof", null]))[0]) > -1)
			return token;
		else
			throw {
				name: "UnexpectedTokenException",
				message: [t[2], t[0]]
			};
	}

	function parse(template, data) {
		var match, tokens = [], rules = [
			{t: "iftag", r: /^(\{[#\?]([a-zA-Z0-9]+)\})/},
			{t: "notiftag", r: /^(\{[!\^]([a-zA-Z0-9]+)\})/},
			{t: "endtag", r: /^(\{\/([a-zA-Z0-9]+)\})/},
			{t: "tag", r: /^(\{([a-zA-Z0-9]+)\})/},
			{t: "text", r: /^([\s\S]*?)\{[#\?!\^\/]?[a-zA-Z0-9]+\}/},
			{t: "text", r: /^([\s\S]*?)$/},
		];

		while (template.length > 0) { // lex
			for (var i = 0; i < rules.length; i ++) {
				if (!(match = template.match(rules[i].r)))
					continue;
				break;
			}

			tokens.push([rules[i].t, match, tokens.length]);
			template = template.substring(match[1].length);
		}

		return statement(tokens, [data]); // parse
	}

	function statement (tokens, scope) {
		var token, result = "";

		while (tokens.length > 0) {
			token = accept(tokens, ["iftag", "notiftag", "text", "tag"]);

			if (["iftag", "notiftag"].indexOf(token[0]) > -1)
				result += condition(tokens, token, scope);
			else if (token[0] == "tag")
				result += tag(token, scope);
			else if (token[0] == "text")
				result += token[1][1];
		}

		return result;
	}

	function condition (tokens, start, scope) {
		var contents = [], end, value, statements, result = "";

		for (;;) {
			end = accept(tokens, ["iftag", "notiftag", "endtag", "text", "tag"]);

			if (end[0] == "endtag" && start[1][2] == end[1][2])
				break;

			contents.push(end);
		}

		if (start[0] == "iftag" && !!(value = get(scope, start[1][2]))) {
			if (Array.isArray(value)) {
				buffer = "";

				for (var i = 0; i < value.length; i ++) {
					statements = contents.slice(0);

					if (typeof value[i] === "object")
						scope.push(value[i]);

					result += statement(statements, scope);

					scope.pop();
				}

				return result;
			}

			return statement(contents, scope);
		} else if (start[0] == "notiftag" && !get(scope, start[1][2]))
			return statement(contents, scope);

		return "";
	}

	function tag (token, scope) {
		if (!!get(scope, token[1][2]))
			return get(scope, token[1][2]);

		return "";
	}

	return parse;
})();