react usememo

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Naughty Nightingale answered on March 12, 2021 Popularity 10/10 Helpfulness 3/10

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const memoizedValue = useMemo(() => computeExpensiveValue(a, b), [a, b]);

Returns a memoized value.

Pass a “create” function and an array of dependencies. useMemo will only recompute the memoized value when one of the dependencies has changed. This optimization helps to avoid expensive calculations on every render.

Remember that the function passed to useMemo runs during rendering. Don’t do anything there that you wouldn’t normally do while rendering. For example, side effects belong in useEffect, not useMemo.

If no array is provided, a new value will be computed on every render.

You may rely on useMemo as a performance optimization, not as a semantic guarantee. In the future, React may choose to “forget” some previously memoized values and recalculate them on next render, e.g. to free memory for offscreen components. Write your code so that it still works without useMemo — and then add it to optimize performance.

Popularity 10/10 Helpfulness 3/10 Language javascript

Source: Grepper

Tags: javascript react-usememo

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Contributed on Mar 12 2021

Naughty Nightingale

0 Answers Avg Quality 2/10

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usememo

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useMemo is a hook that takes a function and a list of dependencies as arguments, and returns a value that is the result of calling the function. The value is stored in a cache and is only re-computed if one of the dependencies has changed.

Here is the syntax for useMemo:

import { useMemo } from 'react';

function MyComponent(props) {
  // Calculate the value of `result` using an expensive computation
  // The value will only be re-computed if `props.x` or `props.y` changes
  const result = useMemo(() => {
    // Perform the expensive computation here
    let sum = 0;
    for (let i = 0; i < props.x; i++) {
      sum += i;
    }
    return sum;
  }, [props.x, props.y]);

  return (
    <div>
      The sum of the first {props.x} positive integers is {result}.
    </div>
  );
}

In this example, the component calculates the sum of the first props.x positive integers using an expensive loop. The value is stored in a cache and is only re-computed if either props.x or props.y changes. This can help to improve the performance of the component by avoiding unnecessary re-calculations.

Popularity 10/10 Helpfulness 4/10 Language javascript

Source: Grepper

Tags: javascript j

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Contributed on Jan 06 2023

vip_codes

0 Answers Avg Quality 2/10

useMemo

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const memoizedResult = useMemo(() => {
  return expensiveFunction(propA, propB);
}, [propA, propB]);

Popularity 10/10 Helpfulness 3/10 Language javascript

Source: dmitripavlutin.com

Tags: javascript j

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Contributed on Sep 05 2021

Inexpensive Ibex

0 Answers Avg Quality 2/10

usememo react

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import React, { memo, useMemo, useState } from 'react'

const Heading = memo(({ style, title }) => {
  console.log('Rendered:', title)

  return <h1 style={style}>{title}</h1>
})

export default function App() {
  const [count, setCount] = useState(0)

  const normalStyle = {
    backgroundColor: 'teal',
    color: 'white',
  }

  const memoizedStyle = useMemo(() => {
    return {
      backgroundColor: 'red',
      color: 'white',
    }
  }, [])

  return (
    <>
      <button
        onClick={() => {
          setCount(count + 1)
        }}
      >
        Increment {count}
      </button>
      <Heading style={memoizedStyle} title="Memoized" />
      <Heading style={normalStyle} title="Normal" />
    </>
  )
}

Popularity 10/10 Helpfulness 3/10 Language javascript

Source: www.react.express

Tags: hook

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Contributed on Nov 08 2022

Mehedi Islam Ripon

0 Answers Avg Quality 2/10

useMemo

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/*
Pass a “create” function and an array of dependencies. 
useMemo will only recompute the memoized value when one 
of the dependencies has changed. This optimization helps 
to avoid expensive calculations on every render.
*/
const memoizedValue = useMemo(() => computeExpensiveValue(a, b), [a, b]);

Popularity 10/10 Helpfulness 2/10 Language javascript

Source: reactjs.org

Tags: javascript j

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Contributed on Aug 12 2021

Poised Puffin

0 Answers Avg Quality 2/10

usememo

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//when just a or b dependency change memoizedValie is work
// we are doing for when your component rendering but this memorizedValue to complexity have
// and you just want to render this complexity codes when a or b changes

const memoizedValue = useMemo(() => {
return computeExpensiveValue(a, b)

}, [a, b]);

Popularity 10/10 Helpfulness 2/10 Language javascript

Source: reactjs.org

Tags: javascript j

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Contributed on Sep 15 2022

myagizmaktav

0 Answers Avg Quality 2/10

React useMemo Hook

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//A poor performing function. The expensiveCalculation function runs on every render
import { useState } from "react";
import ReactDOM from "react-dom/client";

const App = () => {
  const [count, setCount] = useState(0);
  const [todos, setTodos] = useState([]);
  const calculation = expensiveCalculation(count);

  const increment = () => {
    setCount((c) => c + 1);
  };
  const addTodo = () => {
    setTodos((t) => [...t, "New Todo"]);
  };

  return (
    <div>
      <div>
        <h2>My Todos</h2>
        {todos.map((todo, index) => {
          return <p key={index}>{todo}</p>;
        })}
        <button onClick={addTodo}>Add Todo</button>
      </div>
      <hr />
      <div>
        Count: {count}
        <button onClick={increment}>+</button>
        <h2>Expensive Calculation</h2>
        {calculation}
      </div>
    </div>
  );
};

const expensiveCalculation = (num) => {
  console.log("Calculating...");
  for (let i = 0; i < 1000000000; i++) {
    num += 1;
  }
  return num;
};

const root = ReactDOM.createRoot(document.getElementById('root'));
root.render(<App />);

Popularity 10/10 Helpfulness 1/10 Language javascript

Source: Grepper

Tags: hook

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Contributed on May 24 2022

naly moslih

0 Answers Avg Quality 2/10

when to use usememo

Comment

https://beta.reactjs.org/learn/you-might-not-need-an-effect

Popularity 10/10 Helpfulness 1/10 Language whatever

Source: Grepper

Tags: whatever whateve

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Contributed on Mar 01 2023

ShanK

0 Answers Avg Quality 2/10

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