Conventions used

There are a number of text conventions used throughout this book.

Code in text: Indicates code words in text, database table names, folder names, filenames, file extensions, pathnames, dummy URLs, user input, and Twitter handles. Here is an example: “ In order to make the code easier to follow, we’ll switch on the lowercased version of tagName.”

A block of code is set as follows:

<script>
  // handle receiving messages from iframe -> parent
  const allowedMessageOrigins = ['http://127.0.0.1:8000'];
  window.addEventListener('message', (event) => {
    if (!allowedMessageOrigins.includes(event.origin)) {
      console.warn(
        `Dropping message due to non-allowlisted origin ${event.origin}`,
        event,
      );
      return;
    }
    // no change to the rest of the message handler
  });
</script>

Bold: Indicates a new term, an important word, or words that you see onscreen. For instance, words in menus or dialog boxes appear in bold. Here is an example: “When opening the select, things seem to work ok, we’re seeing the Fruit: prefix for all the options.”

Tips or important notes

Appear like this.