nolimits4web/swiper · warning

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Error message

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What it means

showWarning (src/shared/utils.ts:147-153) is Swiper's single warning funnel: every loop/grid advisory string is passed to console.warn(text) at line 149. The body is wrapped in try { ... } catch { /* err */ }, so if console is missing or console.warn throws, the warning is silently swallowed with no re-throw and no fallback channel. This makes the function an observability choke point: the other four warnings in this batch (and all Swiper runtime advisories) surface only if console.warn is actually callable in the host environment.

Source

Thrown at src/shared/utils.ts:149

        : []),
    );
  }
  return false;
}

export function elementIsChildOf(el: Element, parent: Element): boolean {
  let isChild = parent.contains(el);
  if (!isChild && parent instanceof HTMLSlotElement) {
    const children = [...parent.assignedElements()];
    isChild = children.includes(el);
    if (!isChild) isChild = elementIsChildOfSlot(el, parent);
  }
  return isChild;
}

export function showWarning(text: string): void {
  try {
    console.warn(text);
  } catch {
    // err
  }
}

export function createElement<K extends keyof HTMLElementTagNameMap>(
  tag: K,
  classes?: string | string[],
): HTMLElementTagNameMap[K];
export function createElement(tag: string, classes?: string | string[]): HTMLElement;
export function createElement(tag: string, classes: string | string[] = []): HTMLElement {
  const el = document.createElement(tag);
  el.classList.add(...(Array.isArray(classes) ? classes : classesToTokens(classes)));
  return el;
}

// Viewport-relative on purpose: every caller either compares against viewport quantities
// or adds window.scrollX/Y itself, so folding the scroll offset in here double-counts.

View on GitHub (pinned to 6138c2a685)

Solutions

1. Do not delete, null, or reassign console.warn to a throwing function in any environment where Swiper runs; if you must silence noise, filter by message prefix instead of throwing.
2. If running in SSR/Node, ensure globalThis.console is a real console (e.g. keep Node's default) or polyfill console.warn before constructing the Swiper instance.
3. To capture Swiper warnings deterministically, wrap console.warn before new Swiper(...) and forward matching messages, since the internal try/catch will otherwise swallow failures.
4. Treat Swiper warnings as config defects: fix the upstream loop/grid config (see errors 1-4) so showWarning is never called, rather than relying on console visibility.

Example fix

// before -- Swiper warnings go to console.warn and may be swallowed by showWarning's try/catch
const swiper = new Swiper(el, { loop: true });
// after -- intercept console.warn before init to capture every Swiper advisory
const captured: string[] = [];
const origWarn = console.warn.bind(console);
console.warn = (m: unknown) => {
  if (typeof m === 'string' && m.startsWith('Swiper')) captured.push(m);
  origWarn(m);
};
const swiper = new Swiper(el, { loop: true });

// Run once, before any Swiper instance is created, to ensure warnings can surface
function ensureSwiperConsole(): void {
  const g = globalThis as { console?: Partial<Console> };
  if (typeof g.console?.warn !== 'function') {
    g.console = {
      ...(g.console ?? {}),
      warn: (m?: unknown) => process.stderr.write(String(m ?? '') + '\n'),
    } as Console;
  }
}
ensureSwiperConsole();

function hasWarnableConsole(c: unknown): c is Console & { warn: (m?: unknown) => void } {
  return typeof c === 'object' && c !== null && typeof (c as Console).warn === 'function';
}

// showWarning swallows internally, so intercept BEFORE it runs
const swiperWarnings: string[] = [];
const origWarn = console.warn.bind(console);
console.warn = (m?: unknown) => {
  if (typeof m === 'string' && m.startsWith('Swiper')) swiperWarnings.push(m);
  origWarn(m);
};
try {
  const swiper = new Swiper(el, params);
} finally {
  console.warn = origWarn; // restore
}

When it happens

Trigger: console.warn(text) is invoked with any Swiper advisory (e.g. a loop warning). The catch block executes only when the host cannot warn: console is undefined (some SSR/node setups without a console polyfill), console.warn has been deleted or reassigned to a throwing stub, a sandboxed iframe restricts the console, or CSP/lockdown config makes console.warn throw. In a normal browser the call succeeds and the string is printed as a console warning.

Common situations: Server-side rendering where globalThis.console is absent or shimmed; unit tests that stub console.warn to throw on noise; iframe sandboxes (allow-scripts without a full console); CI pipelines that fail on any console.warn where the silent catch then hides which advisory fired; overridden/monkey-patched consoles in analytics-heavy apps.

AI-assisted analysis of nolimits4web/swiper@6138c2a685 (2026-08-12). Data as JSON: /api/errors/9f1b95548c7b3181. Report an issue: GitHub.