Nunjucks Custom Tag

sample.js

// Ref 1: https://mozilla.github.io/nunjucks/api.html#custom-tags
// Ref 2: https://dreamonward.com/2019/12/05/nunjucks-custom-tag/
const nunjucks = require("nunjucks")

const DATA = "# Header 1\n\n{% test %}\nHere is Test Section\n{% endtest %}"

class CustomTag {
  constructor() {
    this.tags = ["test"]
  }

  parse(parser, nodes) {
    const token = parser.nextToken();  // Get the tag token

    // Parse the args and move after the block end.
    const args = parser.parseSignature(null, true);
    parser.advanceAfterBlockEnd(token.value);

    // Parse the body
    const body = parser.parseUntilBlocks('test', 'endtest');
    parser.advanceAfterBlockEnd();

    // Actually do work on block body and arguments
    return new nodes.CallExtension(this, 'run', args, [body]);
  };

  run(context, bodyCallback) {
    const body = bodyCallback()
    const html = `<p>${body}</p>`

    return new nunjucks.runtime.SafeString(html)
  }
}

const env = new nunjucks.Environment()
env.addExtension("test", new CustomTag())

console.log(env.renderString(DATA, null));