Memo Once, No Dependencies

TODO: collapasable, copyable, download, etc

Can I useMemo without any dependencies in React? I'm trying to only run something once across component lifecyclesYes, you can use useMemo without specifying any dependencies in React, but the intended way to run something only once across component lifecycles and to memoize a value for the lifetime of a component is slightly different than just omitting the dependencies array.

When you use useMemo (or useEffect, for that matter) and you want something to run only once, you would typically provide an empty dependencies array ([]). This effectively tells React to only run the useMemo callback on the initial render and not on subsequent re-renders, since there are no dependencies that it is watching for changes.

const memoizedValue = useMemo(() => {
  // Perform expensive calculation or operation here
  return result;
}, []); // Empty dependencies array means this runs once

However, it's crucial to note that this approach memoizes the value for re-renders of the component, not across different instances of the component or across unmounting and mounting cycles. If the component unmounts and then mounts again (for example, if it's removed from the DOM and then re-added), the useMemo function will run again.

If you're looking for a way to truly run something only once across all lifecycles and instances of a component, that's a bit against the typical grain of how React components are supposed to work, as they are intended to be isolated and not have side effects persist outside their lifecycle.

For global or persistent state that should survive across component mounts and unmounts, you might consider using a different pattern, such as:

• Global state management (using Context API, Redux, etc.) to hold the state outside of the component.
• Static variables outside of the component if it's truly constant and doesn't depend on the component's props or state.
• Custom hooks with internal static variables or refs that preserve values across re-renders and can encapsulate the logic for determining whether to recompute or perform operations.

Each of these approaches has different implications for how your component interacts with the rest of your application, so the best choice depends on your specific requirements and architecture.

Memo Once, No Dependencies created at Tue Jan 20 1970 19:37:42 GMT+0000 (Coordinated Universal Time)