Sketch plugin code: alternative to console.log

const {toArray} = require('util');

// returns a timestamp
const timeStamp = () => {
  const now = new Date();
  return `${'0'.concat(now.getHours()).slice(-2)}:${'0'.concat(now.getMinutes()).slice(-2)}:${'0'.concat(now.getSeconds()).slice(-2)}.${now.getMilliseconds().toString().concat('000').slice(0,3)}`;
}

// Assumes an existing text layer called 'debug_output' on the current page that's NOT in a group or artboard
// parameters: the Sketch page object, the thing (or an array of things) to log, whether or not to clear previous logs
const logIt = (page, args, clear = false) => {
  // convert args to array if it's not already an array
  args = [].concat(args || []);
  // find the 'debug_output' text layer on page
  const debugTextLayer = toArray(page.layers()).filter(item => item.name() == 'debug_output')[0];
  if (debugTextLayer === undefined) {
    return undefined;
  }
  // clear out previous logs
  if (clear) {
    debugTextLayer.setStringValue("Debug output:");
  }
  // construct debug string from args[], delimited by the pipe character
  if (args.length > 0) {
    let debugString = `(${timeStamp()}): `;
    for (const arg of args) {
      debugString = `${debugString}${arg.toString()} | `;
    }
    // get rid of trailing pipe delimiter
    debugString = debugString.slice(0, debugString.length - 3);
    // add debug string to debug_output text layer
    debugTextLayer.setStringValue(`${debugTextLayer.stringValue()}\n${debugString}`);
  }
}

// Example usage
const myFunction = (context) => {
  const doc = context.document;
  const page = doc.currentPage();
  // clear previous log entries and log the name of the current page
  logIt(page, page.name(), true);
  // log both the name of the current page and a date object
  logIt(page, [page.name, new Date()]);
}

// output (in debug_output text layer):
//
// Debug output:
// (16:01:36.902): Page 2
// (16:01:36.903): Page 2 | Wed Jan 22 2020 16:01:36 GMT-0800 (PST)