Remove extra li inside of ul in handlebarjs

I have a handlebar html

<ul><li>{{#listConstruct product}}{{this}}{{/listConstruct}}</li></ul>

Need to have output like this

<ul>
<li>Pen</li>
<li>Pencil</li>
<li>Notebook</li>
</ul>

I wrote a listConstruct helper like this.

Handlebars.registerHelper('listConstruct', function(items) {
   let res = '';
    items.forEach((val)=>{res+= '<li>'+val+'</li>'});
   return res;
 });

But this result in output like this

<ul><li><li>Pen</li><li>Pencil</li><li>Notebook</li></li></ul>

How to remove the extra li inside of UL.

I truly do not understand why you cannot use a simple #each as in:

<ul>
  {{#each items}}
    <li>{{this}}</li>
  {{/each}}
</ul>

If you absolutely must add your template within the <li>, then you can do the following. You can achieve your desired result by joining all of the items in your array together with </li><li> so that the finished string looks like Pen</li><li>Pencil</li><li>Notebook. This string, once injected into the template's <li> will produce your desired, valid HTML. Note: You will need to use Handlebars' SafeString utility function so as not to escape the HTML tags in the helper's return value.

<!-- begin snippet: js hide: false console: true babel: false -->

<!-- language: lang-js -->

const template = Handlebars.compile(`<ul><li>{{#listConstruct product}}{{this}}{{/listConstruct}}</li></ul>`);

const product = [
  'Pen',
  'Pencil',
  'Notebook'
];

Handlebars.registerHelper('listConstruct', function (items, options) {
  return options.fn(new Handlebars.SafeString(items.join('</li><li>')));
});

document.body.innerHTML = template({ product });

<!-- language: lang-html -->

<script src="https://cdnjs.cloudflare.com/ajax/libs/handlebars.js/4.7.7/handlebars.min.js"></script>

<!-- end snippet -->