useRef Hook

Q: What is the difference between useRef and useState?

useRef stores a mutable value that persists across renders but does not trigger re-renders when updated. useState stores a value that triggers a re-render when updated via its setter. Use useRef for values the UI does not display; use useState for values the UI reflects.

Q: Why is my DOM ref null when I try to access it?

A DOM ref is null until React attaches it after the first render. Access DOM refs inside useEffect (which runs after mount) or behind a null check. On the first render, the JSX hasn't been committed to the DOM yet.

Q: Gotcha: Why doesn't updating ref.current cause my component to re-render?

Updating .current mutates the object in place; React has no way to detect this change. There is no setter function -- you assign directly: ref.current = newValue. If the UI should reflect the value, use useState instead.

Q: How do I store the previous value of a prop or state using useRef?

The ref holds the value from the previous render because useEffect runs after render.

Q: When should I use a callback ref instead of an object ref?

Use a callback ref ref={(node) => { ... }} when you need to run code when an element attaches or detaches (e.g., conditional rendering). Object refs only give you the element reference but don't notify you of changes. Callback refs are useful for measuring elements or integrating with non-React libraries.

Q: Gotcha: Is it safe to read ref.current during render?

Reading ref.current during render (outside useEffect or event handlers) can give inconsistent results. React may render your component multiple times (concurrent features), and the ref value could be from a different render pass. Read refs only in effects or event handlers.

Q: How do I focus an input on mount using useRef?

The ref is null until mount, so access it inside useEffect with optional chaining.

Hold a mutable value that persists across renders without causing re-renders.

Recipe

Quick-reference recipe card - copy-paste ready.

// Mutable instance variable
const renderCount = useRef(0);
renderCount.current += 1;
 
// DOM element reference
const inputRef = useRef<HTMLInputElement>(null);
inputRef.current?.focus();
 
// Store previous value
const prevValue = useRef(value);
useEffect(() => { prevValue.current = value; });

When to reach for this: You need to access a DOM element directly, store a mutable value that should not trigger re-renders, or keep track of a previous value.

Working Example

"use client";
 
import { useEffect, useRef, useState } from "react";
 
export function Stopwatch() {
  const [elapsed, setElapsed] = useState(0);
  const [running, setRunning] = useState(false);
  const intervalRef = useRef<ReturnType<typeof setInterval> | null>(null);
 
  useEffect(() => {
    if (running) {
      intervalRef.current = setInterval(() => {
        setElapsed((prev) => prev + 10);
      }, 10);
    }
    return () => {
      if (intervalRef.current) clearInterval(intervalRef.current);
    };
  }, [running]);
 
  const reset = () => {
    setRunning(false);
    setElapsed(0);
  };
 
  const minutes = Math.floor(elapsed / 60000);
  const seconds = Math.floor((elapsed % 60000) / 1000);
  const ms = Math.floor((elapsed % 1000) / 10);
 
  return (
    <div className="space-y-3">
      <p className="text-3xl font-mono tabular-nums">
        {String(minutes).padStart(2, "0")}:{String(seconds).padStart(2, "0")}.
        {String(ms).padStart(2, "0")}
      </p>
      <div className="flex gap-2">
        <button
          onClick={() => setRunning((r) => !r)}
          className="px-3 py-1 border rounded"
        >
          {running ? "Stop" : "Start"}
        </button>
        <button onClick={reset} className="px-3 py-1 border rounded">
          Reset
        </button>
      </div>
    </div>
  );
}

What this demonstrates:

Using useRef to store the interval ID so it can be cleared later
The ref persists across renders without triggering re-renders when updated
ReturnType<typeof setInterval> provides the correct type for the timer ID
The ref is cleaned up in the effect's cleanup function

Deep Dive

How It Works

useRef returns a mutable object with a single .current property
The object reference is stable - React returns the same object on every render
Updating .current does not trigger a re-render
Unlike useState, there is no setter function - you mutate .current directly
The ref object is created once on mount and persists until the component unmounts

Parameters & Return Values

Parameter	Type	Description
`initialValue`	`T`	Initial value assigned to `.current`

Return	Type	Description
`ref`	`{ current: T }`	Mutable ref object

Variations

Focus an input on mount:

const inputRef = useRef<HTMLInputElement>(null);
 
useEffect(() => {
  inputRef.current?.focus();
}, []);
 
return <input ref={inputRef} />;

Track previous value:

function usePrevious<T>(value: T): T | undefined {
  const ref = useRef<T | undefined>(undefined);
  useEffect(() => {
    ref.current = value;
  });
  return ref.current;
}

Store latest callback (avoids stale closures):

const callbackRef = useRef(callback);
useEffect(() => {
  callbackRef.current = callback;
});
 
// Use callbackRef.current in event handlers or timers

Measure a DOM element:

const divRef = useRef<HTMLDivElement>(null);
 
useEffect(() => {
  if (divRef.current) {
    const { width, height } = divRef.current.getBoundingClientRect();
    setSize({ width, height });
  }
}, []);

TypeScript Notes

// DOM ref - use `null` as initial value with element type
const divRef = useRef<HTMLDivElement>(null);
// divRef.current is HTMLDivElement | null
 
// Mutable ref - pass the type as generic
const countRef = useRef<number>(0);
// countRef.current is number
 
// Distinction: useRef<T>(null) creates RefObject<T> (readonly .current)
// useRef<T | null>(null) creates MutableRefObject<T | null>
// For DOM refs, use the first pattern; for mutable values, use the second

Gotchas

Reading refs during render - Accessing ref.current during rendering (outside useEffect or event handlers) can give inconsistent results. Fix: Read refs in effects or event handlers only.
Expecting re-renders on mutation - Updating ref.current does not re-render the component. Fix: If the UI should update, use useState instead.
Null ref on first render - A DOM ref is null until React attaches it after the first render. Fix: Access DOM refs inside useEffect or after a null check.
Ref vs. state confusion - Storing UI-visible data in a ref means the display never updates. Fix: Use refs only for values that do not need to be displayed or that drive side effects.
Callback refs vs. object refs - Object refs cannot notify you when the element changes (e.g., conditional rendering). Fix: Use a callback ref ref={(node) => { ... }} when you need to react to attachment/detachment.

Alternatives

Alternative	Use When	Don't Use When
`useState`	The value should trigger a re-render when it changes	You need a silent mutable container
Callback ref	You need to run code when a ref attaches or detaches	You just need a stable reference to an element
`document.getElementById`	Outside React (rare)	Inside React components - use refs instead
Module-level variable	Value is shared across all component instances	Value should be per-component-instance

Why refs instead of module variables? Module-level variables are shared across all instances of a component. Refs are per-instance - each mounted component gets its own .current.

FAQs

What is the difference between useRef and useState?

useRef stores a mutable value that persists across renders but does not trigger re-renders when updated.
useState stores a value that triggers a re-render when updated via its setter.
Use useRef for values the UI does not display; use useState for values the UI reflects.

Why is my DOM ref null when I try to access it?

A DOM ref is null until React attaches it after the first render.
Access DOM refs inside useEffect (which runs after mount) or behind a null check.
On the first render, the JSX hasn't been committed to the DOM yet.

How do I type a DOM ref vs a mutable value ref in TypeScript?

// DOM ref: use null initial, get RefObject<T> (readonly .current)
const inputRef = useRef<HTMLInputElement>(null);
 
// Mutable ref: include null in the generic union
const countRef = useRef<number | null>(null);
// countRef.current is number | null (mutable)

Gotcha: Why doesn't updating ref.current cause my component to re-render?

Updating .current mutates the object in place; React has no way to detect this change.
There is no setter function -- you assign directly: ref.current = newValue.
If the UI should reflect the value, use useState instead.

How do I store the previous value of a prop or state using useRef?

function usePrevious<T>(value: T): T | undefined {
  const ref = useRef<T | undefined>(undefined);
  useEffect(() => {
    ref.current = value;
  });
  return ref.current;
}

The ref holds the value from the previous render because useEffect runs after render.

When should I use a callback ref instead of an object ref?

Use a callback ref ref={(node) => { ... }} when you need to run code when an element attaches or detaches (e.g., conditional rendering).
Object refs only give you the element reference but don't notify you of changes.
Callback refs are useful for measuring elements or integrating with non-React libraries.

Can I use useRef to store a timer or interval ID?

const intervalRef = useRef<ReturnType<typeof setInterval> | null>(null);
 
useEffect(() => {
  intervalRef.current = setInterval(tick, 1000);
  return () => {
    if (intervalRef.current) clearInterval(intervalRef.current);
  };
}, []);

Yes, this is a common pattern. The ref persists the ID across renders so cleanup can access it.

Gotcha: Is it safe to read ref.current during render?

Reading ref.current during render (outside useEffect or event handlers) can give inconsistent results.
React may render your component multiple times (concurrent features), and the ref value could be from a different render pass.
Read refs only in effects or event handlers.

Why use a ref instead of a module-level variable?

Module-level variables are shared across all instances of a component.
Refs are per-instance -- each mounted component gets its own .current.
If two instances of a component use the same module variable, they overwrite each other.

How do I focus an input on mount using useRef?

const inputRef = useRef<HTMLInputElement>(null);
 
useEffect(() => {
  inputRef.current?.focus();
}, []);
 
return <input ref={inputRef} />;

The ref is null until mount, so access it inside useEffect with optional chaining.

What is the "latest callback" ref pattern and why is it useful?

Store the latest version of a callback in a ref, updating it on every render.
Use callbackRef.current in timers or event listeners to always call the latest version.
This avoids stale closures without adding the callback to dependency arrays.

useState - when you need the value to trigger re-renders
useEffect - access DOM refs inside effects after mount
useCallback - stabilize callbacks that are stored in refs
useId - generate unique IDs for DOM elements instead of using refs for identification

Recipe

Quick-reference recipe card - copy-paste ready.

// Mutable instance variable
const renderCount = useRef(0);
renderCount.current += 1;
 
// DOM element reference
const inputRef = useRef<HTMLInputElement>(null);
inputRef.current?.focus();
 
// Store previous value
const prevValue = useRef(value);
useEffect(() => { prevValue.current = value; });

When to reach for this: You need to access a DOM element directly, store a mutable value that should not trigger re-renders, or keep track of a previous value.

Working Example

"use client";
 
import { useEffect, useRef, useState } from "react";
 
export function Stopwatch() {
  const [elapsed, setElapsed] = useState(0);
  const [running, setRunning] = useState(false);
  const intervalRef = useRef<ReturnType<typeof setInterval> | null>(null);
 
  useEffect(() => {
    if (running) {
      intervalRef.current = setInterval(() => {
        setElapsed((prev) => prev + 10);
      }, 10);
    }
    return () => {
      if (intervalRef.current) clearInterval(intervalRef.current);
    };
  }, [running]);
 
  const reset = () => {
    setRunning(false);
    setElapsed(0);
  };
 
  const minutes = Math.floor(elapsed / 60000);
  const seconds = Math.floor((elapsed % 60000) / 1000);
  const ms = Math.floor((elapsed % 1000) / 10);
 
  return (
    <div className="space-y-3">
      <p className="text-3xl font-mono tabular-nums">
        {String(minutes).padStart(2, "0")}:{String(seconds).padStart(2, "0")}.
        {String(ms).padStart(2, "0")}
      </p>
      <div className="flex gap-2">
        <button
          onClick={() => setRunning((r) => !r)}
          className="px-3 py-1 border rounded"
        >
          {running ? "Stop" : "Start"}
        </button>
        <button onClick={reset} className="px-3 py-1 border rounded">
          Reset
        </button>
      </div>
    </div>
  );
}

What this demonstrates:

Using useRef to store the interval ID so it can be cleared later
The ref persists across renders without triggering re-renders when updated
ReturnType<typeof setInterval> provides the correct type for the timer ID
The ref is cleaned up in the effect's cleanup function

Deep Dive

How It Works

useRef returns a mutable object with a single .current property
The object reference is stable - React returns the same object on every render
Updating .current does not trigger a re-render
Unlike useState, there is no setter function - you mutate .current directly
The ref object is created once on mount and persists until the component unmounts

Parameters & Return Values

Parameter	Type	Description
`initialValue`	`T`	Initial value assigned to `.current`

Return	Type	Description
`ref`	`{ current: T }`	Mutable ref object

Variations

Focus an input on mount:

const inputRef = useRef<HTMLInputElement>(null);
 
useEffect(() => {
  inputRef.current?.focus();
}, []);
 
return <input ref={inputRef} />;

Track previous value:

function usePrevious<T>(value: T): T | undefined {
  const ref = useRef<T | undefined>(undefined);
  useEffect(() => {
    ref.current = value;
  });
  return ref.current;
}

Store latest callback (avoids stale closures):

const callbackRef = useRef(callback);
useEffect(() => {
  callbackRef.current = callback;
});
 
// Use callbackRef.current in event handlers or timers

Measure a DOM element:

const divRef = useRef<HTMLDivElement>(null);
 
useEffect(() => {
  if (divRef.current) {
    const { width, height } = divRef.current.getBoundingClientRect();
    setSize({ width, height });
  }
}, []);

TypeScript Notes

// DOM ref - use `null` as initial value with element type
const divRef = useRef<HTMLDivElement>(null);
// divRef.current is HTMLDivElement | null
 
// Mutable ref - pass the type as generic
const countRef = useRef<number>(0);
// countRef.current is number
 
// Distinction: useRef<T>(null) creates RefObject<T> (readonly .current)
// useRef<T | null>(null) creates MutableRefObject<T | null>
// For DOM refs, use the first pattern; for mutable values, use the second

Gotchas

Reading refs during render - Accessing ref.current during rendering (outside useEffect or event handlers) can give inconsistent results. Fix: Read refs in effects or event handlers only.
Expecting re-renders on mutation - Updating ref.current does not re-render the component. Fix: If the UI should update, use useState instead.
Null ref on first render - A DOM ref is null until React attaches it after the first render. Fix: Access DOM refs inside useEffect or after a null check.
Ref vs. state confusion - Storing UI-visible data in a ref means the display never updates. Fix: Use refs only for values that do not need to be displayed or that drive side effects.
Callback refs vs. object refs - Object refs cannot notify you when the element changes (e.g., conditional rendering). Fix: Use a callback ref ref={(node) => { ... }} when you need to react to attachment/detachment.

Alternatives

Alternative	Use When	Don't Use When
`useState`	The value should trigger a re-render when it changes	You need a silent mutable container
Callback ref	You need to run code when a ref attaches or detaches	You just need a stable reference to an element
`document.getElementById`	Outside React (rare)	Inside React components - use refs instead
Module-level variable	Value is shared across all component instances	Value should be per-component-instance

Why refs instead of module variables? Module-level variables are shared across all instances of a component. Refs are per-instance - each mounted component gets its own .current.

FAQs

What is the difference between useRef and useState?

useRef stores a mutable value that persists across renders but does not trigger re-renders when updated.
useState stores a value that triggers a re-render when updated via its setter.
Use useRef for values the UI does not display; use useState for values the UI reflects.

Why is my DOM ref null when I try to access it?

A DOM ref is null until React attaches it after the first render.
Access DOM refs inside useEffect (which runs after mount) or behind a null check.
On the first render, the JSX hasn't been committed to the DOM yet.

How do I type a DOM ref vs a mutable value ref in TypeScript?

// DOM ref: use null initial, get RefObject<T> (readonly .current)
const inputRef = useRef<HTMLInputElement>(null);
 
// Mutable ref: include null in the generic union
const countRef = useRef<number | null>(null);
// countRef.current is number | null (mutable)

Gotcha: Why doesn't updating ref.current cause my component to re-render?

Updating .current mutates the object in place; React has no way to detect this change.
There is no setter function -- you assign directly: ref.current = newValue.
If the UI should reflect the value, use useState instead.

How do I store the previous value of a prop or state using useRef?

function usePrevious<T>(value: T): T | undefined {
  const ref = useRef<T | undefined>(undefined);
  useEffect(() => {
    ref.current = value;
  });
  return ref.current;
}

The ref holds the value from the previous render because useEffect runs after render.

When should I use a callback ref instead of an object ref?

Use a callback ref ref={(node) => { ... }} when you need to run code when an element attaches or detaches (e.g., conditional rendering).
Object refs only give you the element reference but don't notify you of changes.
Callback refs are useful for measuring elements or integrating with non-React libraries.

Can I use useRef to store a timer or interval ID?

const intervalRef = useRef<ReturnType<typeof setInterval> | null>(null);
 
useEffect(() => {
  intervalRef.current = setInterval(tick, 1000);
  return () => {
    if (intervalRef.current) clearInterval(intervalRef.current);
  };
}, []);

Yes, this is a common pattern. The ref persists the ID across renders so cleanup can access it.

Gotcha: Is it safe to read ref.current during render?

Reading ref.current during render (outside useEffect or event handlers) can give inconsistent results.
React may render your component multiple times (concurrent features), and the ref value could be from a different render pass.
Read refs only in effects or event handlers.

Why use a ref instead of a module-level variable?

Module-level variables are shared across all instances of a component.
Refs are per-instance -- each mounted component gets its own .current.
If two instances of a component use the same module variable, they overwrite each other.

How do I focus an input on mount using useRef?

const inputRef = useRef<HTMLInputElement>(null);
 
useEffect(() => {
  inputRef.current?.focus();
}, []);
 
return <input ref={inputRef} />;

The ref is null until mount, so access it inside useEffect with optional chaining.

What is the "latest callback" ref pattern and why is it useful?

Store the latest version of a callback in a ref, updating it on every render.
Use callbackRef.current in timers or event listeners to always call the latest version.
This avoids stale closures without adding the callback to dependency arrays.

useState - when you need the value to trigger re-renders
useEffect - access DOM refs inside effects after mount
useCallback - stabilize callbacks that are stored in refs
useId - generate unique IDs for DOM elements instead of using refs for identification

useRef Hook

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useRef Hook