Its a Custom Web Component. Do not use the constructor directly with the new keyword. Instead, use one of the 3 following methods:

Create the Web Component and call its init method:

const myBlock = document.createElement("a-block").init(config)

Or use the shorthand for it:

const myBlock = createBlock({
  padding: "10px",
  items: [
      // Block items...
  ]
})

myBlock.render()

Or directly declare the config inside a container component:

const myPanel = createPanel({
  items: [
      {
          type: "block",
          title: "Foo",
          items: [
              // Block items...
          ]
      }
  ]
})
myPanel.render()

IMPORTANT

When embedded into another container, the item type defaults to "block", which means it's not necessary to set the type property for block elements:

const myPanel = createPanel({
  items: [
      {
          // This item has no type: KissJS will generate a block by default
          title: "Foo",
          items: [
              // Block items...
          ]
      }
  ]
})
myPanel.render()