withastro/astro · error · TypeError

First argument must be a string

Error message

First argument must be a string

What it means

`parseInlineStyles` is a small hand-written CSS inline-style parser. Its contract requires the first argument be a string; any other type (number, undefined, null, object) throws `TypeError('First argument must be a string')`. An empty string short-circuits to `[]`.

Source

Thrown at packages/integrations/markdoc/src/html/css/parse-inline-styles.ts:55

const NEWLINE = '\n';
const FORWARD_SLASH = '/';
const ASTERISK = '*';
const EMPTY_STRING = '';

// types
const TYPE_COMMENT = 'comment';
const TYPE_DECLARATION = 'declaration';

/**
 * @param {String} style
 * @param {Object} [options]
 * @return {Object[]}
 * @throws {TypeError}
 * @throws {Error}
 */
export function parseInlineStyles(style, options) {
	if (typeof style !== 'string') {
		throw new TypeError('First argument must be a string');
	}

	if (!style) return [];

	options = options || {};

	/**
	 * Positional.
	 */
	let lineno = 1;
	let column = 1;

	/**
	 * Update lineno and column based on `str`.
	 *
	 * @param {String} str
	 */
	function updatePosition(str) {

View on GitHub (pinned to d081033d5f)

Solutions

1. Guard the call: `if (typeof style === 'string') parseInlineStyles(style)`.
2. Coerce with a default: `parseInlineStyles(style ?? '')` (empty string returns `[]`).
3. Fix the upstream caller to only pass strings.

Example fix

// before
parseInlineStyles(node.attributes.style)

// after
parseInlineStyles(typeof node.attributes.style === 'string' ? node.attributes.style : '')

function safeParseInlineStyles(style: unknown) {
  return typeof style === 'string' ? parseInlineStyles(style) : [];
}

function isStyleString(v: unknown): v is string {
  return typeof v === 'string';
}

When it happens

Trigger: Calling `parseInlineStyles(value)` where `value` is `undefined`, `null`, a number, an object, or any non-string. Common when reading an attribute that may be absent (`element.attributes.style` returning undefined) and passing it through without coercion.

Common situations: Markdoc/MDX node whose `style` attribute is optional and not always present. Passing a parsed AST node instead of its string value. Defensive code path that forgets a null check.

Related errors

• CannotDetermineWeightAndStyleFromFontFile
• ${cssTransformErrors[0].message}
• Invalid transition name {${transitionName}}
• (Uncaught error) Partial tag requires a 'file' attribute
• **${relativePartialPath}** contains invalid content: Could n

AI-assisted analysis of withastro/astro@d081033d5f (2026-08-12). Data as JSON: /api/errors/ac68c0161c1678bb. Report an issue: GitHub.