# Add Query Parameters

To add query parameters to the URL, update the PageReference `state` property. The key-value pairs of the `state` property are serialized to URL query parameters. The query parameters describe the page and form a more specific URL that the user can save or bookmark.

Keep these behaviors in mind when working with the `state` property.

- You can’t directly change the `pageReference` object. To update the `state`, create a new `pageReference` object, and copy the values using `Object.assign({}, pageReference)`.
- `state` parameters must be namespaced. For example, a managed package with the namespace `abc` with a parameter `accountId` is represented as `abc__accountId`. The namespace for custom components is `c__`.Parameters without a namespace are reserved for Salesforce use. This namespace restriction is introduced under a critical update in Winter ’19 and enforced in Summer ’19.
- Since the key-value pairs of `PageReference.state` are serialized to URL query parameters, all the values must be strings.
- Code that consumes values from `state` must parse the value into its proper format.
- To delete a value from the `state` object, define it as `undefined`.

If your component uses the `lightning:hasPageReference` or `lightning:isUrlAddressable` interfaces, always implement a change handler. When the target of a navigation action maps to the same component, the routing container might simply update the `pageReference` attribute value instead of recreating the component. In this scenario, a change handler ensures that your component reacts correctly.