Javascript: What is the difference between Function and Class

With the release of ECMAScript 6 on June 2015, Javascript classes syntax was introduced.

This syntax:

class Polygon {
      constructor(width, height) {
        this.width = width;
        this.height = height;
      }
}

is basically same as:

function Polygon(width, height) {
    this.width = width;
    this.height = height;
}

So what is the benefit of using class instead of traditional function? And in what condition I should use class instead of function?