<a class="collapsible" style="cursor: pointer;"><span>read more</span></a>

var coll = document.getElementsByClassName("collapsible");
var i;

for (i = 0; i < coll.length; i++) {
  coll[i].addEventListener("click", function() {
    this.classList.toggle("active");
    var content = this.previousElementSibling;
    if (content.style.display === "block") {
      content.style.display = "none";
      coll[i].innerText="read more";    //if I use coll[0] then it works for first element, but I want to use it for multiple elements
    } else {
      content.style.display = "block";
      coll[i].innerText="read less";
    }
  });
}