_.reverseTemplate() attempts to reverse engineer the original object used to generate a rendered underscore.js template output by comparing the output string to the template string.

underscore.reverseTemplate.js

/* Extend the underscore global object with the following method:
 *
 * https://gist.github.com/adamblank/7328089
 *
 * reverseTemplate attempts to reverse engineer the original object used to generate
 * the rendered output by comparing the output string to the underscore template string.
 *
 * Paramaters
 * - renderedOutput - the string that was generated from the template
 * - template - the template string used to generate the compiled underscore template (not the compiled template function.)
 *
 * Dependencies
 * - underscore.js
 *
 * Limitations
 * - This method can only reverse engineer templates that only use interpolation
 * - Values used in template must be top-level properties only (i.e. { prop: 'value' } NOT { obj: { prop: 'value }} )
 * - Interpolation values cannot be right next to each other (e.g. <%= name %><%= age %>)
 */

_.reverseTemplate = function(renderedOutput, template) {
	function extractValue(renderedOutput, template, resultObj) {
		//get underscore's template interpolation regular expression (remove global flag)
		var regex = _.templateSettings.interpolate instanceof RegExp ? new RegExp(_.templateSettings.interpolate.source) : _.templateSettings.interpolate,
			match = template.match(regex),
			prop,
			templateSplit,
			secondSplitPivot,
			value;

		if (!match) {
			return resultObj;
		}
		//get the specifc template interpolation property
		prop = match[1].replace(/ /g,''); 
		templateSplit = template.split(match[0]);
		//grab subsection between this interpolation placeholder and the next (if any)
		secondSplitPivot = templateSplit[1].split(regex)[0];
		//slice off everything before interpolation value
		value = renderedOutput.replace(templateSplit[0], '');
		//if theres more after the value, slice it off also
		if (secondSplitPivot) {
			value = value.split(secondSplitPivot)[0];
		}
		resultObj[prop] = value;
		return extractValue(renderedOutput, template.replace(regex, value), resultObj);
	}
	return extractValue(renderedOutput, template, {});
}

/*
 * Test
 */

//change underscore's templating interpolation delimiter to something nicer (not required)
_.templateSettings = {
	interpolate: /\{\{(.+?)\}\}/g
};

_.reverseTemplate('this is a test to make sure extractTemplateValues works', 'this is a {{ activity }} to make sure {{ plugin }} {{ status }}');

//outputs: Object {activity: "test", plugin: "extractTemplateValues", status: "works"}