useState with URLs: How to persist state with useSearchParams

The React useState Hook is a great way to persist state inside the context of a component in React. This post demonstrates a simple React Hook that stores state in the URL query string, building on top of the React Router useSearchParams Hook.

The useState Hook

Usage of the useState Hook looks like this:

const [greeting, setGreeting] = useState('hello world');

// ....

setGreeting('hello John'); // will set greeting to 'hello John'

However, there is a disadvantage to using useState; that state is not persistent and not shareable. So if you want others to see what you can see in an application, you’re reliant on them carrying out the same actions that got your application into its current state.

Doing that can be time-consuming and error-prone, so wouldn’t it be great if there was a simple way to share state?

A stateful URL

An effective way to share state between users, without needing a backend for persistence, is with the URL. A URL can contain the required state in the form of the route and the query string/search parameters. The search parameters are particularly powerful as they are entirely generic and customizable.

Thanks to the URLSearchParams API, it’s possible to manipulate the query string without round-tripping to the server. This is a primitive upon which we can build; as long as the URL limit (around 2,000 characters) is not exceeded, we’re free to persist state in a URL.

Consider:
https://our-app.com/?greeting=hi
The above URL is storing a single piece of state: the greeting.

Now consider:
https://our-app.com?greeting=hi&name=john
The above URL goes further and stores multiple pieces of state: the greeting and name.

The useSearchParams Hook

If you’re working with React, React Router makes consuming state in the URL, particularly in the form of a query string or search parameters, straightforward. It achieves this with the useSearchParams Hook:

import { useSearchParams } from "react-router-dom";

const [searchParams, setSearchParams] = useSearchParams();

const greeting = searchParams.get('greeting');

// ...

setSearchParams({ 'greeting': 'bonjour' }); // will set URL like so https://our-app.com?greeting=bonjour - this value will feed through to anything driven by the URL

This is a great mechanism for persisting state both locally and in a shareable way.

A significant benefit of this approach is that it doesn’t require posting to the server. It’s just using browser APIs like the URLSearchParams API. Changing a query string parameter happens entirely locally and instantaneously.

The useSearchParamsState Hook

What the useSearchParams Hook doesn’t do is maintain other query string or search parameters.

If we are maintaining multiple pieces of state in your application, that will likely mean multiple query string or search parameters. What would be quite useful, then, is a Hook that allows us to update state without losing other states.

Furthermore, it would be great if we didn’t have to first acquire the searchParams object and then manipulate it. It’s time for our useSearchParamsState Hook:

import { useSearchParams } from "react-router-dom";

export function useSearchParamsState(
    searchParamName: string,
    defaultValue: string
): readonly [
    searchParamsState: string,
    setSearchParamsState: (newState: string) => void
] {
    const [searchParams, setSearchParams] = useSearchParams();

    const acquiredSearchParam = searchParams.get(searchParamName);
    const searchParamsState = acquiredSearchParam ?? defaultValue;

    const setSearchParamsState = (newState: string) => {
        const next = Object.assign(
            {},
            [...searchParams.entries()].reduce(
                (o, [key, value]) => ({ ...o, [key]: value }),
                {}
            ),
            { [searchParamName]: newState }
        );
        setSearchParams(next);
    };
    return [searchParamsState, setSearchParamsState];
}

The above Hook can roughly be thought of as useState<string>, but storing state in the URL.
Let’s think about how it works. When initialized, the Hook takes two parameters:

• searchParamName: the name of the query string parameter where state is persisted
• defaultValue: the fallback value if there’s no value in the query string

The Hook then goes on to wrap the useSearchParams Hook. It interrogates the searchParams for the supplied searchParamName, and if it isn’t present, falls back to the defaultValue.

The setSearchParamsState method definition looks somewhat complicated, but essentially all it does is get the contents of the existing search parameters and apply the new state for the current property.

It’s probably worth pausing here a second to observe an opinion that’s lurking in this implementation: it is actually valid to have multiple values for the same search parameter. While this is possible, it’s somewhat rare for this to be used; this implementation only allows for a single value for any given parameter, as that is quite useful behavior.

With all this in place, we have a Hook that can be used like so:

const [greeting, setGreeting] = useSearchParamsState("greeting", "hello");

The above code returns a greeting value, which is derived from the greeting search parameter. It also returns a setGreeting function, which allows us to set the greeting value. This is the same API as useState, so it should feel idiomatic to React users. Tremendous!

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Performance: useSearchParamsState Hook vs. useSearchParams Hook

At this point, you might be wondering “why don’t we always use the useSearchParamsState Hook?” It all boils down to one reason: performance. The useSearchParamsState Hook is slower than the useState Hook. Let’s think about why.

If we’re using the useState Hook, then ultimately a variable is being updated inside the program that represents our application. This is internal state. However, the story is slightly different for the useSearchParamsState Hook.

The useSearchParamsState Hook is built upon the useSearchParams Hook in React Router, as we’ve seen. If we look at the implementation of that Hook, we can see that it relies on various browser APIs, such as location and History:

The upshot here is that the state of the useSearchParamsState Hook is external to our application. It may not feel this way because we haven’t had to set up a database or an API, its state is external. State lives in the browser’s APIs, and with that comes a performance penalty. Here’s what happens every time we change state:

• The useSearchParams Hook in React Router invokes the History API
• The browser updates the URL
• The React Router instance running at the root of the application detects changes in the location.search and surfaces a new value for the application
• The code in the application that depends upon this value reacts

The above is slower than just invoking useState and relying upon a local variable. However, it’s not overwhelmingly slower. I’ve generally not had an issue because browsers are very fast these days. Still, if you’re intending to write code that is as performant as possible you may want to avoid this Hook.

Anything that involves an external API, even if it’s an API that lives in the browser, will be slower than local variables. I would expect there to be very few applications for which this is a significant factor, but it is still worth considering.

Persisting query strings across your site

Now, we have this exciting mechanism set up that allows us to store state in our URL and, as a consequence, easily share state by sending someone the URL.

What would also be useful is a way to navigate around our site without losing that state. Imagine I have a date range selected and stored in my URL. As I click around from screen to screen, I want to persist that — I don’t want to have to reselect the date range on each screen.

How can we do this? Well, it turns out to be quite easy. All we need is the useLocation Hook and the corresponding location.search property. That represents the query string, so every time we render a link, we just include that like so:

const [location] = useLocation();

return (<Link to={`/my-page${location.search}`}>Page</>)

Now as we navigate around our site, that state will be maintained.

Conclusion

In this post, we’ve created a useSearchParamsState Hook, which allows state to be persisted to URLs for sharing purposes.