eyaltoledano/claude-task-master · error · Error

Format must be a string

Error message

Format must be a string

What it means

ProgressBarFactory.createBar() validates that the bar format is a string before handing it to multibar.create, since cli-progress formats are template strings. Non-string formats (undefined, objects) would silently corrupt rendering, so it throws immediately.

Source

Thrown at src/progress/tracker-ui.js:19

import chalk from 'chalk';

/**
 * Factory for creating progress bar elements
 */
class ProgressBarFactory {
	constructor(multibar) {
		if (!multibar) {
			throw new Error('Multibar instance is required');
		}
		this.multibar = multibar;
	}

	/**
	 * Creates a progress bar with the given format
	 */
	createBar(format, payload = {}) {
		if (typeof format !== 'string') {
			throw new Error('Format must be a string');
		}

		const bar = this.multibar.create(
			1, // total
			1, // current
			{},
			{
				format,
				barsize: 1,
				hideCursor: true,
				clearOnComplete: false
			}
		);

		bar.update(1, payload);
		return bar;
	}

View on GitHub (pinned to c0c98d367c)

Solutions

1. Pass a string format, e.g. createBar('{bar} {percentage}%').
2. Check that any format constant you reference is actually imported and defined.
3. Coerce/validate dynamic formats: typeof fmt === 'string' ? fmt : DEFAULT_FORMAT.
4. Trace whether createHeader/createRow/createBorder received a bad argument upstream.

Example fix

// before
// factory.createBar(SOME_FORMAT) // SOME_FORMAT undefined
// after
// import { SOME_FORMAT } from './formats.js'; // ensure defined
// factory.createBar(SOME_FORMAT || '{bar} {percentage}%');

function safeCreateBar(factory, format, payload) {
  const fmt = typeof format === 'string' && format.length ? format : '{bar} {percentage}% | {value}/{total}';
  return factory.createBar(fmt, payload);
}

function isBarFormat(f) {
  return typeof f === 'string' && f.length > 0;
}

try {
  factory.createBar(format);
} catch (e) {
  if (e.message === 'Format must be a string') {
    return factory.createBar(DEFAULT_BAR_FORMAT);
  }
  throw e;
}

When it happens

Trigger: factory.createBar(undefined) or createBar(someObject) — e.g. a format constant not imported/defined, or a config value that isn't a string; called internally by createHeader, createRow, and createBorder.

Common situations: Missing import of a format constant (undefined passed through), building format strings dynamically and getting non-string results, renamed/removed format helpers after a version upgrade.

Understand the failure class

Background: Invalid argument type errors: "must be of type string", "expected X, got Y", and ERR_INVALID_ARG_TYPE explained — this error's family across 15 libraries.

Related errors

• Spinner messages must be an array
• Multibar instance is required
• MFA_VERIFICATION_FAILED
• Failed to initialize services: ${(error as Error).message}
• Invalid format: ${options.format}. Valid formats are: text,

AI-assisted analysis of eyaltoledano/claude-task-master@c0c98d367c (2026-08-29). Data as JSON: /api/errors/1862f5df3091fae8. Report an issue: GitHub.