A simple Javascript function that linkifies a tweet object's text based on that tweet's entities.

linkifyTweet.js

/**
 * A simple Javascript function that linkifies a tweet object's text based on that tweet's entities.
 * 
 * More info about Tweet Entities: https://dev.twitter.com/docs/tweet-entities .
 * 
 * NOTE: You may need to add "include_entities=1" or "include_entities=true" to your API request.
 */
function linkifyTweet(tweet){
	if(!tweet.entities){
		return tweet.text;
	}
	
	var container = cache = {};
	
	for(var i=0;i<tweet.entities.hashtags.length;i++){
		cache = tweet.entities.hashtags[i];
		container[cache.indices[0]] = [cache.indices[1], '<a href="https://twitter.com/search?q='+cache.text+'">#'+cache.text+'</a>'];
	}
	
	for(var i=0;i<tweet.entities.user_mentions.length;i++){
		cache = tweet.entities.user_mentions[i];
		container[cache.indices[0]] = [cache.indices[1], '<a href="https://twitter.com/'+cache.screen_name+'">@'+cache.screen_name+'</a>'];
	}
	
	for(var i=0;i<tweet.entities.urls.length;i++){
		cache = tweet.entities.urls[i];
		container[cache.indices[0]] = [cache.indices[1], '<a href="'+cache.url+'">'+(cache.display_url||cache.url)+'</a>'];
	}
	
	var orig = tweet.text;
	
	cache = orig;
	
	for(var i=0;i<tweet.text.length;i++){
		if(container[i]){
			cache = cache.replace(orig.substring(i, container[i][0]), container[i][1]);
		}
	}
	
	return cache;
}