yew/website/docs/concepts/function-components/hooks/use-memo.mdx

---
title: 'use_memo'
---

`use_memo` is used for obtaining an immutable reference to a memoized value.
Its state persists across renders.
Its value will be recalculated only if any of the dependencies changes value.

`use_memo` can be useful for keeping things in scope for the lifetime of the component, so long as
you don't store a clone of the resulting `Rc` anywhere that outlives the component.

```rust
use yew::{function_component, html, use_memo, use_state, Callback, Html, Properties};

#[derive(PartialEq, Properties)]
pub struct Props {
    pub step: usize,
}

#[function_component(UseMemo)]
fn ref_hook(props: &Props) -> Html {
    // Will only get recalculated if `props.step` value changes
    let message = use_memo(
        |step| format!("{}. Do Some Expensive Calculation", step),
        props.step
    );

    html! {
        <div>
            <span>{ (*message).clone() }</span>
        </div>
    }
}
```