Thead parsing returns null

May 10, 2023

I have the following function:

function parseMarkupToDOM(markup) {
    return new DOMParser().parseFromString(markup, "text/html").body.firstElementChild;
}

When passing most elements, it works just fine. For instance:

parseMarkupToDOM(`<button>myButton</button>`); // returns a proper DOM element
parseMarkupToDOM(`<h1>myHeading</h1>`); // returns a proper DOM element

However, when I try to parse a thead into a DOM element, I get null:

parseMarkupToDOM(`
    <thead>
        <tr></tr>
        <tr></tr>
    </thead>
`); // returns null

I thought that maybe thead cannot be the child of body, but I am not sure how to get around it, and was not able to find any useful information about this issue. Any idea?

>Solution :

The DOMParser method you are using parses the HTML string into an HTML document, which includes a DOCTYPE declaration, html element, head element, and body element. The firstElementChild property returns the first child of the body element, which in the case of your thead example is null, because thead is not a valid child of body.

To parse the thead element and return it as a valid DOM element, you can wrap the thead element inside a table element (which in your case you don’t want to do, so you achieve this by creating a template element ) and then parse the whole string as follows:

function parseMarkupToDOM(markup) {
  const template = document.createElement('template');
  template.innerHTML = markup.trim();
  return template.content.firstChild;
}

const theadElement = parseMarkupToDOM(`
    <thead>
        <tr></tr>
        <tr></tr>
    </thead>
`);
console.log(theadElement);