How the condition will work if the attribute value and the ID value are the same through the loop

Question

<style>

    .heading {
        color: red;
    }
    
    .button {
        font-size: 18px;
    }
    
    .skyblue {
        background-color: skyblue;
    }
</style>

If <h1> tag's "data-mh" and <button> tag's id has similar attribute than if I click on the button the button background-color will change. And the attribute will print on the P tag. My code is working with first button but it's not working with the second or othersbuttons. /* how can do it by loop */

<h1 class="heading" data-mh="item1">Hello World</h1>
<button class="button" id="item1">Click Here</button>

<h1 class="heading" data-mh="item2">Hello World</h1>
<button class="button" id="item2">Click Here</button>

<h1 class="heading" data-mh="item3">Hello World</h1>
<button class="button" id="item3">Click Here</button>

<p id="demo"></p>
<!-- This Paragraph tag will print my attribute -->

<!-- HTML End -->

<script>
    var x = document.querySelector(".heading").getAttribute("data-mh"); // This variable is to get Attribute of "data-mh"
    var y = document.querySelector(".button"); // Button selection. By clicking this button I will get print my Attribute
    var z = y.getAttribute("id"); // Getting button id to compaire with "data-mh" attribute
    y.onclick = function() {
        //If X (ID) and Z (Attribute) matching then working this Condition
        if (x == z) {
            y.classList.toggle("skyblue");
            document.getElementById("demo").innerHTML = x+" "+z; // This line of code will print my Attribute on P tag
        }
    }
</script>

Answer 1

const buttons = document.querySelectorAll(".button");
const headings = document.querySelectorAll(".heading");

for (const button of buttons) {
  for (const heading of headings) {
    button.addEventListener("click", (event) => {
      const x = button.getAttribute("id");
      const z = heading.getAttribute("data-mh");
      if (x == z) {
        button.classList.toggle("skyblue");
        document.getElementById("demo").innerHTML = x + " " + z;
      }
    });
  }
}