JS Truncate without cutting off words

truncate.js

var truncate = function(text, characterLimit) {
        if( !text || text.length < characterLimit ){ return text; }
        var expressionString = "^(.{" + characterLimit + "}[^\\s]*).*";
        var expression = new RegExp(expressionString);
        var truncatedText = text.replace(expression, "$1");
        return truncatedText +  '...'
}