How to set a text bold in javascript code example

Example 1: make text bold js

<button onclick="myFunction()">Try it</button>

<p >Make text bold <span id="demo">Text Bold</p>

<script>
function myFunction() {
  document.getElementById("demo").style.fontWeight = "900";
}
</script>

Example 2: javascript add text to bold tag

TextBox.innerHTML = "Hello";