Code to add inline click-to-tweet links in WordPress while using the text editor. Full tutorial here: http://zoerooney.com/blog/tutorials/inline-click-to-tweet-functionality/

tweet-quicktag.php

function add_tweet_quicktag(){ ?>
	<script>
		// create a new quicktag button labeled "tweet"
		QTags.addButton( 'quicktweet', 'tweet', selection_callback );

		// on click, it triggers this callback:
	    function selection_callback(e, c, ed) {

	    	// we want to grab the selected text and we're going to get a URL as well
	        var selection, postURL, t = this;
	        if ( ed.canvas.selectionStart !== ed.canvas.selectionEnd ) {
	            
	            // if there's selected text, grab it
	            selection = ed.canvas.value.substring  (ed.canvas.selectionStart, ed.canvas.selectionEnd);
	            
	            // trigger the prompt for URL
	            postURL = prompt('Enter URL to include in Tweet');
	            
	            // if there's no URL that's ok, it'll just be blank
	            if ( postURL === null ) return;

	            // generate the tag that will go before the selection
	            // include the selected text and the URL, if one was given
	            t.tagStart = '<span class="twitterHighlight" data-tweet="' + selection + '" data-shorturl="' + postURL + '">';

	            // generate the tag that will go after the selection
	            t.tagEnd = '</span>';
	        
	        } else {

	        	// if there's no selected text, show an alert message
	        	alert('Please select the text you\'d like to tweet');
	        	return false;
	        }
	        QTags.TagButton.prototype.callback.call(t, e, c, ed);
	    };
	</script>
<?php 
} // end the function
add_action( 'admin_print_footer_scripts', 'add_tweet_quicktag' );

tweet.js

(function() {
	// This first block generates the link markup from the data attributes
	// This is very heavily influenced by code from https://github.com/tevko/WP-Tweetable-Text
	var wpt = window.wpt = window.wpt || {};
	wpt.TweetHighlight = {
		init: function() {
			var s = this.settings;
			
			// this next bit loops through each ".twitterHighlight" selector,
			// so that they each get the link markup with their own data
			Array.prototype.forEach.call(document.querySelectorAll('.twitterHighlight'), function(el, i){
		
				var thisEl = el, // this is grabbing the current span element
				content = thisEl.textContent, // for this element, grab the text within
				tweet = thisEl.getAttribute('data-tweet'), // also grab the data-tweet content
				postURL = thisEl.getAttribute('data-shorturl'), // and the URL
				filteredTweet = encodeURIComponent(tweet), // encode the tweet for URL use
				filteredURL = encodeURIComponent(postURL), // encode the URL
				
				// the next line creates the markup for the link
				// note that it's adding the Twitter icon from Font Awesome http://fortawesome.github.io/Font-Awesome/
				template = '<a target=_blank href="http://twitter.com/share?text=' + filteredTweet + '&via=zoe_rooney&url=' + filteredURL + '">' + content + ' <i class="fa fa-twitter"></i></a>',
				
				// the next line actually generates the markup on the selected element
				link = thisEl.innerHTML = template;
			});
		}
	};

	wpt.TweetHighlight.init();
})();

jQuery(document).ready(function($){
	// This block handles the click action on those generated links
	$('.twitterHighlight a').click(function(e){
		e.preventDefault; // first, don't do the default link action
		var link = $(this).attr('href'); // get the link href attribute (the URL)
		popup = window.open( 
			// pop open a little window with that link
			link, 'tweet', 'height=450, width=750'
		); 
		popup.focus(); // put the focuson that window so user can send the tweet
	});
});