How can I cut a string after X characters?

Simply

  var trunc = "abcdef".substr(0, 3) + "\u2026";

var trucatedText = yourtext.substring(0, 3) + '...';  // substring(from, to);

The other answers are great, but they always add an ellipsis. The following will only add an ellipsis if the string is too long:

function truncateText(text, length) {
  if (text.length <= length) {
    return text;
  }

  return text.substr(0, length) + '\u2026'
}

let truncated;
truncated = truncateText('Hello, World!', 10);
console.log(truncated);
truncated = truncateText('Hello, World!', 50);
console.log(truncated);

Sth like this?

var text= "This is your text";
var stripHere = 7;
var shortText = text.substring(0, stripHere) + "...";

alert(shortText);

http://jsfiddle.net/ThKsw/