Overflow Text JS

index.html

<p data-overflow>Olá Daniel Nass, como está você meu filho?</p>

overflow.js

String.prototype.overflow = function (text = '...', start = 10, end = 4) {
  let startText = this.substr(0, start);
  let endText = this.substr(-Math.abs(end));
  
  if (this.length <= (parseInt(start) + parseInt(end) + text.length)) {
    return this;
  }
  
  return `${startText.trim()}${text}${endText.trim()}`;
}

let overflowTexts = document.querySelectorAll('[data-overflow]');

[].slice.call(overflowTexts).forEach(el => {
  let text = el.getAttribute('data-overflow-text') || '...';
  let start = el.getAttribute('data-overflow-start') || 10;
  let end = el.getAttribute('data-overflow-end') || 4;
  
  el.innerText = el.innerText.overflow(text, start, end);
});

Demo Online: http://codepen.io/CezarLuiz0/pen/dOqgJO?editors=1010