Make React useEffect hook not run on initial render

Question

According to the docs:

componentDidUpdate() is invoked immediately after updating occurs. This method is not called for the initial render.

We can use the new useEffect() hook to simulate componentDidUpdate(), but it seems like useEffect() is being ran after every render, even the first time. How do I get it to not run on initial render?

As you can see in the example below, componentDidUpdateFunction is printed during the initial render but componentDidUpdateClass was not printed during the initial render.

function ComponentDidUpdateFunction() {
  const [count, setCount] = React.useState(0);
  React.useEffect(() => {
    console.log("componentDidUpdateFunction");
  });

  return (
    <div>
      <p>componentDidUpdateFunction: {count} times</p>
      <button
        onClick={() => {
          setCount(count + 1);
        }}
      >
        Click Me
      </button>
    </div>
  );
}

class ComponentDidUpdateClass extends React.Component {
  constructor(props) {
    super(props);
    this.state = {
      count: 0,
    };
  }

  componentDidUpdate() {
    console.log("componentDidUpdateClass");
  }

  render() {
    return (
      <div>
        <p>componentDidUpdateClass: {this.state.count} times</p>
        <button
          onClick={() => {
            this.setState({ count: this.state.count + 1 });
          }}
        >
          Click Me
        </button>
      </div>
    );
  }
}

ReactDOM.render(
  <div>
    <ComponentDidUpdateFunction />
    <ComponentDidUpdateClass />
  </div>,
  document.querySelector("#app")
);

<script src="https://unpkg.com/react@16.7.0-alpha.0/umd/react.development.js"></script>
<script src="https://unpkg.com/react-dom@16.7.0-alpha.0/umd/react-dom.development.js"></script>

<div id="app"></div>

Answer 1

We can use the useRef hook to store any mutable value we like, so we could use that to keep track of if it's the first time the useEffect function is being run.

If we want the effect to run in the same phase that componentDidUpdate does, we can use useLayoutEffect instead.

Example

const { useState, useRef, useLayoutEffect } = React;

function ComponentDidUpdateFunction() {
  const [count, setCount] = useState(0);

  const firstUpdate = useRef(true);
  useLayoutEffect(() => {
    if (firstUpdate.current) {
      firstUpdate.current = false;
      return;
    }

    console.log("componentDidUpdateFunction");
  });

  return (
    <div>
      <p>componentDidUpdateFunction: {count} times</p>
      <button
        onClick={() => {
          setCount(count + 1);
        }}
      >
        Click Me
      </button>
    </div>
  );
}

ReactDOM.render(
  <ComponentDidUpdateFunction />,
  document.getElementById("app")
);

<script src="https://unpkg.com/react@16.7.0-alpha.0/umd/react.development.js"></script>
<script src="https://unpkg.com/react-dom@16.7.0-alpha.0/umd/react-dom.development.js"></script>

<div id="app"></div>

Answer 2

You can turn it into custom hook (new documentation page: Reusing Logic with Custom Hooks), like so:

import React, { useEffect, useRef } from 'react';

const useDidMountEffect = (func, deps) => {
    const didMount = useRef(false);

    useEffect(() => {
        if (didMount.current) func();
        else didMount.current = true;
    }, deps);
}

export default useDidMountEffect;

Usage example:

import React, { useState, useEffect } from 'react';

import useDidMountEffect from '../path/to/useDidMountEffect';

const MyComponent = (props) => {    
    const [state, setState] = useState({
        key: false
    });    

    useEffect(() => {
        // you know what is this, don't you?
    }, []);

    useDidMountEffect(() => {
        // react please run me if 'key' changes, but not on initial render
    }, [state.key]);    

    return (
        <div>
             ...
        </div>
    );
}
// ...

Answer 3

I made a simple useFirstRender hook to handle cases like focussing a form input:

import { useRef, useEffect } from 'react';

export function useFirstRender() {
  const firstRender = useRef(true);

  useEffect(() => {
    firstRender.current = false;
  }, []);

  return firstRender.current;
}

It starts out as true, then switches to false in the useEffect, which only runs once, and never again.

In your component, use it:

const firstRender = useFirstRender();
const phoneNumberRef = useRef(null);

useEffect(() => {
  if (firstRender || errors.phoneNumber) {
    phoneNumberRef.current.focus();
  }
}, [firstRender, errors.phoneNumber]);

For your case, you would just use if (!firstRender) { ....

Answer 4

Same approach as Tholle's answer, but using useState instead of useRef.

const [skipCount, setSkipCount] = useState(true);

...

useEffect(() => {
    if (skipCount) setSkipCount(false);
    if (!skipCount) runYourFunction();
}, [dependencies])

EDIT

While this also works, it involves updating state which will cause your component to re-render. If all your component's useEffect calls (and also all of its children's) have a dependency array, this doesn't matter. But keep in mind that any useEffect without a dependency array (useEffect(() => {...}) will be run again.

Using and updating useRef will not cause any re-renders.

Answer 5

@ravi, yours doesn't call the passed-in unmount function. Here's a version that's a little more complete:

/**
 * Identical to React.useEffect, except that it never runs on mount. This is
 * the equivalent of the componentDidUpdate lifecycle function.
 *
 * @param {function:function} effect - A useEffect effect.
 * @param {array} [dependencies] - useEffect dependency list.
 */
export const useEffectExceptOnMount = (effect, dependencies) => {
  const mounted = React.useRef(false);
  React.useEffect(() => {
    if (mounted.current) {
      const unmount = effect();
      return () => unmount && unmount();
    } else {
      mounted.current = true;
    }
  }, dependencies);

  // Reset on unmount for the next mount.
  React.useEffect(() => {
    return () => mounted.current = false;
  }, []);
};

Answer 6

function useEffectAfterMount(effect, deps) {
  const isMounted = useRef(false);

  useEffect(() => {
    if (isMounted.current) return effect();
    else isMounted.current = true;
  }, deps);

  // reset on unmount; in React 18, components can mount again
  useEffect(() => {
    isMounted.current = false;
  });
}

We need to return what comes back from effect(), because it might be a cleanup function. But we don't need to determine if it is or not. Just pass it on and let useEffect figure it out.

In an earlier version of this post I said resetting the ref (isMounted.current = false) wasn't necessary. But in React 18 it is, because components can remount with their previous state (thanks @Whatabrain).

Answer 7

a simple way is to create a let, out of your component and set in to true.

then say if its true set it to false then return (stop) the useEffect function

like that:

    import { useEffect} from 'react';
    //your let must be out of component to avoid re-evaluation 
    
    let isFirst = true
    
    function App() {
      useEffect(() => {
          if(isFirst){
            isFirst = false
            return
          }
    
        //your code that don't want to execute at first time
      },[])
      return (
        <div>
            <p>its simple huh...</p>
        </div>
      );
    }

its Similar to @Carmine Tambasciabs solution but without using state :) ‍‍‍‍‍‍ ‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

Answer 8

I thought creating a custom hook would be overkill and I didn't want to muddle my component's readability by using the useLayoutEffect hook for something unrelated to layouts, so, in my case, I simply checked to see if the value of my stateful variable selectedItem that triggers the useEffect callback is its original value in order to determine if it's the initial render:

export default function MyComponent(props) {
    const [selectedItem, setSelectedItem] = useState(null);

    useEffect(() => {
        if(!selectedItem) return; // If selected item is its initial value (null), don't continue
        
        //... This will not happen on initial render

    }, [selectedItem]);

    // ...

}

Answer 9

You can use custom hook to run use effect after mount.

const useEffectAfterMount = (cb, dependencies) => {
  const mounted = useRef(true);

  useEffect(() => {
    if (!mounted.current) {
      return cb();
    }
    mounted.current = false;
  }, dependencies); // eslint-disable-line react-hooks/exhaustive-deps
};

Here is the typescript version:

const useEffectAfterMount = (cb: EffectCallback, dependencies: DependencyList | undefined) => {
  const mounted = useRef(true);

  useEffect(() => {
    if (!mounted.current) {
      return cb();
    }
    mounted.current = false;
  }, dependencies); // eslint-disable-line react-hooks/exhaustive-deps
};

Answer 10

This is the best implementation I've created so far using typescript. Basically, the idea is the same, using the Ref but I'm also considering the callback returned by useEffect to perform cleanup on component unmount.

import {
  useRef,
  EffectCallback,
  DependencyList,
  useEffect
} from 'react';

/**
 * @param effect 
 * @param dependencies
 *  
 */
export default function useNoInitialEffect(
  effect: EffectCallback,
  dependencies?: DependencyList
) {
  //Preserving the true by default as initial render cycle
  const initialRender = useRef(true);

  useEffect(() => {
    let effectReturns: void | (() => void) = () => {};

    // Updating the ref to false on the first render, causing
    // subsequent render to execute the effect
    if (initialRender.current) {
      initialRender.current = false;
    } else {
      effectReturns = effect();
    }

    // Preserving and allowing the Destructor returned by the effect
    // to execute on component unmount and perform cleanup if
    // required.
    if (effectReturns && typeof effectReturns === 'function') {
      return effectReturns;
    } 
    return undefined;
  }, dependencies);
}

You can simply use it, as usual as you use the useEffect hook but this time, it won't run on the initial render. Here is how you can use this hook.

useNoInitialEffect(() => {
  // perform something, returning callback is supported
}, [a, b]);

If you use ESLint and want to use the react-hooks/exhaustive-deps rule for this custom hook:

{
  "rules": {
    // ...
    "react-hooks/exhaustive-deps": ["warn", {
      "additionalHooks": "useNoInitialEffect"
    }]
  }
}

Answer 11

@MehdiDehghani, your solution work perfectly fine, one addition you have to do is on unmount, reset the didMount.current value to false. When to try to use this custom hook somewhere else, you don't get cache value.

import React, { useEffect, useRef } from 'react';

const useDidMountEffect = (func, deps) => {
    const didMount = useRef(false);

    useEffect(() => {
        let unmount;
        if (didMount.current) unmount = func();
        else didMount.current = true;

        return () => {
            didMount.current = false;
            unmount && unmount();
        }
    }, deps);
}

export default useDidMountEffect;

Answer 12

Simplified implementation

import { useRef, useEffect } from 'react';

function MyComp(props) {

  const firstRender = useRef(true);

  useEffect(() => {
    if (firstRender.current) {
      firstRender.current = false;
    } else {
      myProp = 'some val';
    };

  }, [props.myProp])


  return (
    <div>
      ...
    </div>
  )

}

Answer 13

Recently I need to run the first effect on the very first render cause I initialize some stores in it and don't want the app to be rendered without this effect being executed at least one time so I ended up with a new hook usePreffect :) cause it runs effect pre-render

/**
 * Same as useEffect but runs the very first effect synchronously on the first render.
 * Useful for state initializing effects
 */
export const usePreffect = (effect: EffectCallback, deps: any[]): void => {
  const isFirstEffectRun = useRef(true);
  // Run the effect synchronously on the first render and save its cleanup function
  const firstCleanUp = useMemo(() => effect(), []);

  useEffect(() => {
    // Skip the first run and return the previously saved cleanup function
    if (isFirstEffectRun.current) {
      isFirstEffectRun.current = false;
      return firstCleanUp;
    }
    return effect();
  }, deps);
};

Answer 14

For people who are having trouble with React 18 strict mode calling the useeffect on the initial render twice, try this:

// The init variable is necessary if your state is an object/array, because the == operator compares the references, not the actual values.
const init = []; 
const [state, setState] = useState(init);
const dummyState = useRef(init);

useEffect(() => {
  // Compare the old state with the new state
  if (dummyState.current == state) {
    // This means that the component is mounting
  } else {
    // This means that the component updated.
    dummyState.current = state;
  }
}, [state]);

Works in development mode...

function App() {
  const init = []; 
  const [state, setState] = React.useState(init);
  const dummyState = React.useRef(init);

  React.useEffect(() => {
    if (dummyState.current == state) {
      console.log('mount');
    } else {
      console.log('update');
      dummyState.current = state;
    }
  }, [state]);
  
  return (
    <button onClick={() => setState([...state, Math.random()])}>Update state </button>
  );
}

ReactDOM.createRoot(document.getElementById("app")).render(
  <React.StrictMode>
    <App />
  </React.StrictMode>
);

<script crossorigin src="https://unpkg.com/react@18/umd/react.development.js"></script>
<script crossorigin src="https://unpkg.com/react-dom@18/umd/react-dom.development.js"></script>

<div id="app"></div>

And in production.

function App() {
  const init = []; 
  const [state, setState] = React.useState(init);
  const dummyState = React.useRef(init);

  React.useEffect(() => {
    if (dummyState.current == state) {
      console.log('mount');
    } else {
      console.log('update');
      dummyState.current = state;
    }
  }, [state]);
  return (
    <button onClick={() => setState([...state, Math.random()])}>Update state </button>
    );
}

ReactDOM.createRoot(document.getElementById("app")).render(
  <React.StrictMode>
    <App />
  </React.StrictMode>
);

<script crossorigin src="https://unpkg.com/react@18/umd/react.production.min.js"></script>
<script crossorigin src="https://unpkg.com/react-dom@18/umd/react-dom.production.min.js"></script>

<div id="app"></div>

Answer 15

If you want to skip the first render, you can create a state "firstRenderDone" and set it to true in the useEffect with empty dependecy list (that works like a didMount). Then, in your other useEffect, you can check if the first render was already done before doing something.

const [firstRenderDone, setFirstRenderDone] = useState(false);

//useEffect with empty dependecy list (that works like a componentDidMount)
useEffect(() => {
  setFirstRenderDone(true);
}, []);

// your other useEffect (that works as componetDidUpdate)
useEffect(() => {
  if(firstRenderDone){
    console.log("componentDidUpdateFunction");
  }
}, [firstRenderDone]);

Answer 16

All previous are good, but this can be achieved in a simplier way considering that the action in useEffect can be "skipped" placing an if condition(or any other ) that is basically not run first time, and still with the dependency.

For example I had the case of :

1. Load data from an API but my title has to be "Loading" till the date were not there, so I have an array, tours that is empty at beginning and show the text "Showing"
2. Have a component rendered with different information from those API.
3. The user can delete one by one those info, even all making the tour array empty again as the beginning but this time the API fetch is been already done
4. Once the tour list is empty by deleting then show another title.

so my "solution" was to create another useState to create a boolean value that change only after the data fetch making another condition in useEffect true in order to run another function that also depend on the tour length.

useEffect(() => {
  if (isTitle) {
    changeTitle(newTitle)
  }else{
    isSetTitle(true)
  }
}, [tours])

here my App.js

import React, { useState, useEffect } from 'react'
import Loading from './Loading'
import Tours from './Tours'

const url = 'API url'

let newTours

function App() {
  const [loading, setLoading ] = useState(true)
  const [tours, setTours] = useState([])
  const [isTitle, isSetTitle] = useState(false)
  const [title, setTitle] = useState("Our Tours")

  const newTitle = "Tours are empty"

  const removeTours = (id) => {
    newTours = tours.filter(tour => ( tour.id !== id))

    return setTours(newTours)
  }

  const changeTitle = (title) =>{
    if(tours.length === 0 && loading === false){
      setTitle(title)
    }
  }

const fetchTours = async () => {
  setLoading(true)

  try {
    const response = await fetch(url)
    const tours = await response.json()
    setLoading(false)
    setTours(tours)
  }catch(error) {
    setLoading(false)
    console.log(error)
  }  
}


useEffect(()=>{
  fetchTours()
},[])

useEffect(() => {
  if (isTitle) {
    changeTitle(newTitle)
  }else{
    isSetTitle(true)
  }
}, [tours])


if(loading){
  return (
    <main>
      <Loading />
    </main>
  )  
}else{
  return ( 

    <main>
      <Tours tours={tours} title={title} changeTitle={changeTitle}           
removeTours={removeTours} />
    </main>
  )  
 }
}



export default App

Answer 17

    const [dojob, setDojob] = useState(false);

    yourfunction(){
        setDojob(true);
    }

    useEffect(()=>{
        if(dojob){
            yourfunction();
            setDojob(false);
        }
    },[dojob]);

Answer 18

Everyone is giving complicated answers, so I'll just leave it her:

This will render on initial load:

useEffect(() => {
    setData(data)
  });

This will not render on initial load

useEffect(() => {
    setData(data)
  }, []);

Just Javascript stuff :shrug: