Following code truncates a string and will not split words up, and instead discard the word where the truncation occurred. Totally based on Sugar.js source.
function truncateOnWord(str, limit) {
var trimmable = '\u0009\u000A\u000B\u000C\u000D\u0020\u00A0\u1680\u180E\u2000\u2001\u2002\u2003\u2004\u2005\u2006\u2007\u2008\u2009\u200A\u202F\u205F\u2028\u2029\u3000\uFEFF';
var reg = new RegExp('(?=[' + trimmable + '])');
var words = str.split(reg);
var count = 0;
return words.filter(function(word) {
count += word.length;
return count <= limit;
}).join('');
}