<p id="p">Example: <i>italic</i> and <b>bold</b></p>

From <input id="start" type="number" value=1> – To <input id="end" type="number" value=4>
<button id="button">Click to select</button>
<script>
  button.onclick = () => {
    let range = new Range();

    range.setStart(p, start.value);
    range.setEnd(p, end.value);

    // طبّق التحديد، سيُوضَّح لاحقا‏
    document.getSelection().removeAllRanges();
    document.getSelection().addRange(range);
  };
</script>