You can use BSF post processor, which has various scripting language, javascript being one of them.
http://jmeter.apache.org/usermanual/component_reference.html#BSF_PostProcessor
Following is sample javascript from one of my test plan. Note the use of eval, putObject, put, log etc.
log.info("processing image index response");
if ("" != prev.getResponseDataAsString()) {
eval( 'var indexJSON = ' + prev.getResponseDataAsString() );
vars.putObject("indexJSON", indexJSON);
vars.put("currentThumb", "0");
vars.put("currentSlide", "0");
var next_slide_timestamp=indexJSON[0].timestamp;
vars.put("next_slide_timestamp", "0");
var maxSlides=indexJSON.length;
vars.put("maxSlides", maxSlides);
} else {
vars.put("currentThumb", "0");
vars.put("currentSlide", "0");
vars.put("next_slide_timestamp", "0");
vars.put("maxSlides", "0");
log.info("index time : empty response , setting defaults to zero");
}