hast-util-get-attribute

getAttribute and hasAttribute for hast Element type.

In hast, the values of the properties record may be, in addition to the intuitively reasonable string, boolean, number, and (string | number)[], also null and undefined (v2/v3). This is convenient when constructing a tree, but things get a bit complicated when you want to check for presence or obtain a string in a type-safe way.

Below are the results observed from the input/output of hast-util-to-html. You can see that simply relying on truthy/falsy or using String does not yield correct results.

| properties: | toHtml(node) | | ---------------------- | -------------------------- | | undefined (v2) | <div></div> | | {} | <div></div> | | { foo: true } | <div foo></div> | | { foo: false } | <div></div> | | { foo: 42 } | <div foo="42"></div> | | { foo: 0 } | <div foo="0"></div> | | { foo: "bar" } | <div foo="bar"></div> | | { foo: "" } | <div foo=""></div> | | { foo: [42, "bar"] } | <div foo="42 bar"></div> | | { foo: [] } | <div foo=""></div> | | { foo: null } | <div></div> | | { foo: undefined } | <div></div> |