How to handle type of Element.Properties?

[plastic041]

Elements parsed by rehype-parse has Properties, which is typed as Properties | undefined.
However, rehype-parse parses some elements' properties as {}, even if there is no properties at all.

example:

const file = `<img>`;

const logNodes = () => {
  return (tree) => {
    visit(tree, "element", (node) => {
      console.log(`
        ${node.tagName}: ${JSON.stringify(node.properties)}
      `); // should be "img: undefined", but actually logs "img: {}"

      if (node.properties) { //  unnecessary because node.properties is never undefined, but without check it gives type error.
        // do something...
      }
    });
  };
};

unified()
  .use(rehypeParse, { fragment: true })
  .use(logNodes)
  .use(rehypeStringify)
  .process(file);

The problem is, I cannot utilize Properties without checking its type, even if I am sure that it is never undefined.
I am currently using @ts-ignore to supress this issue.
Is this an expected behavior? If it is, how can I handle this without using @ts-ignore?

Codepen link: https://codepen.io/plastic041/pen/powYBXQ

[wooorm]

If you type tree as a hast.Root, everything becomes typed.

properties should always be Properties, not undefined. However, people sometimes forget to add it in their plugins. That’s why it’s recommended to use an if check to make sure it exists

[plastic041]

But you said properties should always be Properties? It is still Properties | undefined.

[wooorm]

Indeed, I said should. But people (who don’t use TypeScript) forget. That’s why it’s typed as optional: to reflect the real world. So that in your code you can check for whether it exists or not and prevent runtime errors.

[plastic041]

I see, I misinterpreted your reply. Thank you for the answer!

[wooorm]

No problem! All the best and good luck.

P.S. we have some guides on unified with typescript: https://unifiedjs.com/learn/guide/syntax-trees-typescript/ and https://unifiedjs.com/learn/recipe/tree-traversal-typescript/. Might be useful?

[plastic041]

Didn't know that. Thanks, I'll check 😀