---
name: "up.Response.prototype.isError"
area: "API"
kind: "Instance method"
parent: "up.Response class"
visibility: "deprecated"
url: "https://unpoly.com/api/up.Response.prototype.isError"
---
<nav aria-label="Unpoly docs">[All docs](https://unpoly.com/index.md) · [up.Response class](https://unpoly.com/api/up.Response.md)</nav>

# up.Response.prototype.isError()

**This feature has been deprecated**. Use `!up.Response#ok` instead.

Load [`unpoly-migrate.js`](https://unpoly.com/changes/upgrading.md) to polyfill deprecated features.

Returns whether the response was not [successful](https://unpoly.com/api/up.Response.prototype.ok.md).

---

## Return value {#return-value}

Type: boolean