I am building an API for my site that grabs an MD file based off URL param (?key=test.md) and then renders it with Marked.js.

My problem is after the API grabs the file and trys to render it i get this error

marked.min.js:6 Uncaught Error: marked(): input parameter is undefined or null
Please report this to https://github.com/markedjs/marked.
    at ie.parse (marked.min.js:6:34386)
    at Object.oe (marked.min.js:6:35545)
    at main.js:14:30

I've checked my variables and network and don't have an idea of what is undefined. Here is m current API code and simple workings.

const queryString = window.location.search;
const urlParams = new URLSearchParams(queryString);

let article = urlParams.get('key');
let pre = `https://mrchaoticx.github.io/Chaotic-Club/articles/${article}`;

let contentID = document.getElementById("content");
let content;
fetch(pre)
  .then(response => response.text())
  .then(data => {content = data})
  .then(data => console.log(content))

contentID.innerHTML = marked.parse(content);

        <div class="content" id="content">
        </div>
        <script src="https://cdnjs.cloudflare.com/ajax/libs/marked/14.1.2/marked.min.js" integrity="sha512-bXyBT2/sYjZg1D7ykDS6eJSE4DFDVPJHvbRAfdfYKr6IusrCz7wAmSm36vz9G8zMob25Rvqu90vft3JI71ygcQ==" crossorigin="anonymous" referrerpolicy="no-referrer"></script>        

Issue

The issue here is that the fetch kicks off a Promise chain that resolves with a value after the rest of the code after it has already completed. You are passing an undefined content value to the marked.parse function.

let contentID = document.getElementById("content");
let content; // <-- (1) declared & undefined

fetch(pre) // <-- (2) start Promise chain
  .then(response => response.text())
  .then(data => {content = data}) // <-- (4) have content now
  .then(data => console.log(content));

contentID.innerHTML = marked.parse(content); // <-- (3) pass undefined

Suggested Solution

Move the DOM mutation into the Promise chain to be used when you have fetched the markdown content.

Example:

fetch(pre)
  .then(response => response.text())
  .then(content => {
    console.log(content);
    const contentID = document.getElementById("content");
    contentID.innerHTML = marked.parse(content);
  });