Attributes.setIfUnset()

The Attributes.setIfUnset() method sets the attribute identified by key to value value but only if it's currently unset (undefined).

Signature

Attributes attributes.setIfUnset(string key, string value)

Example

const attr = new Attributes()
  .setIfUnset('class', 'classA')
  .setIfUnset('class', 'classB')

const class = attr.get('class')
// class now holds: "classA"

Notes

This will never overwrite any value and thus is a safe way to set attributes