"class" keyword generating Syntax error message but Javascript functions

The bigger question is I don't know why you are using the very verbose 'class constructor' method when you could just use a simple function( see below code example).

Since a couple of years back if you use 'React.js' practically every developer using that js framework dropped using the class constructor workflow and opted to use functions when they were introduced, cleaner and simpler in my view.

<script>

const carAge = (year) => {
const date = new Date();
return date.getFullYear() - year
}

document.getElementById("demo").innerHTML = `My car is ${carAge(2014)} years old`;
</script>

No on-point developer uses - + "blah" + "blah" anymore. Template literals ` ` made it far easier to concatenate long strings which include javascript variables/functions.

Just as an aside note I doubt DW will support the new arrow function => (in terms of valid syntax code). If not you can just use the old way of writing a function (which in my opinion is somewhat clearer):

<script>

function carAge(year) {
const date = new Date();
return date.getFullYear() - year
}

document.getElementById("demo").innerHTML = `My car is ${carAge(2014)} years old`;
</script>

CS6 is 10+ year old software that hasn't been updated since its release in 2012.  It's outdated, discontinued and unsupported.  

Why are you using it?   Do yourself a favor and get a modern code editor. 

CODE EDITORS:
-- Adobe Dreamweaver CC - https://www.adobe.com/products/dreamweaver.html
-- Codespaces (free, browser-based) - https://github.com/features/codespaces
-- Nova (Mac only, formerly called Coda) - https://nova.app/
-- Pinegrow - https://pinegrow.com/
-- Sublime Text - http://www.sublimetext.com/
-- Visual Studio Code (free) - https://code.visualstudio.com/
-- Wappler ~ Visual Web App Builder - https://wappler.io/

That said, this code does not throw errors in latest version of Dreamweaver CC (ver 21.3) with Code Linting enabled.

<h1>JavaScript Class Methods</h1>
<p>How to define and use a Class method.</p>

<p id="demo"></p>

<script>
class Car {
  constructor(name, year) {
    this.name = name;
    this.year = year;

  }
  age() {
    const date = new Date();
    return date.getFullYear() - this.year;
  }
}

const myCar = new Car("Ford", 2014);
document.getElementById("demo").innerHTML =
"My car is " + myCar.age() + " years old.";
</script>