Source:

{
  "type": "doc",
  "content": [
    {
      "type": "paragraph",
      "content": [
        {
          "type": "text",
          "text": "That’s a boring paragraph followed by a fenced code block:"
        }
      ]
    },
    {
      "type": "codeBlock",
      "attrs": {
        "language": "javascript"
      },
      "content": [
        {
          "type": "text",
          "text": "for (var i=1; i <= 20; i++)\n{\n  if (i % 15 == 0)\n    console.log(\"FizzBuzz\");\n  else if (i % 3 == 0)\n    console.log(\"Fizz\");\n  else if (i % 5 == 0)\n    console.log(\"Buzz\");\n  else\n    console.log(i);\n}"
        }
      ]
    }
  ]
}

That’s a boring paragraph followed by a fenced code block:

for (var i=1; i <= 20; i++)
{
  if (i % 15 == 0)
    console.log("FizzBuzz");
  else if (i % 3 == 0)
    console.log("Fizz");
  else if (i % 5 == 0)
    console.log("Buzz");
  else
    console.log(i);
}