FAQ: The State Hook - Update Function Component State

This community-built FAQ covers the “Update Function Component State” exercise from the lesson “The State Hook”.

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This exercise can be found in the following Codecademy content:

Learn React

FAQs on the exercise Update Function Component State

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The lesson explains useState() as :

useState() is a JavaScript function defined in the React library.

If it is defined in the React library, and we’re already importing import React from 'react', why do we have to import { setState() } separately from the same library?

1 Like

This lesson says that stateSetter() updates the current value of this state. And by doing so it re-renders the function which is defining the component. Wouldn’t it result in an infinite loop, since we are calling the stateSetter() from inside the function?

you are right, BUT we are calling it under a condition which is onClick so it will only run when you click the button that’s why it’s not an infinite loop. But certainly, you can’t run stateSetter() directly.

1 Like

It’s up to you, you can use React.setState() directly if you don’t want to import “setState” separately :grin:

2 Likes

Why do we need to write:
<button onClick={() => setToggle("On")}>On</button>

Instead of:
<button onClick={setToggle("On")}>On</button>

What is the value of using an arrow function here?

6 Likes

Im wondering the same. Ever figure it out?

If anyone is reading this now…The answer is basically the second option calls setToggle immediately when ever button is rendered to the screen.
the original sets the onClick function to an unnamed arrow function that calls setToggle when the button is clicked.

8 Likes

When trying to run this exercise, I encounter the error
“Oops! The test returned an error. Maybe you have a syntax error, or a typo.
Browserslist: caniuse-lite is outdated. Please run:
npx [email protected] --update-db”
Is this an error originating with my computer, or with codecademy? I tried running the command in terminal, but nothing happened, and I encountered the same error when I tried the exercise on a different computer. I can’t figure out how to proceed with the lesson, as my code will not run.

1 Like

Great question! I’m wondering the same thing. It’s frustrating that the reason for this is never explained in the course, but you are just expected to know it after a certain lesson…

React is the default import from ‘react’. If you want to import anything else, you need to put it in the braces. You wouldn’t want to import everything automatically, as that could cause unexpected namespace collisions.

1 Like

I found the use of the anonymous arrow function quite confusing. There is a good explanation here: React - why use anonymous function for event handler? - #2 by jenovs - JavaScript - The freeCodeCamp Forum

(See the response from DanCouper)

2 Likes

I have a few questions about this lesson. Hopefully someone will be able to help me.

  1. The destructing array already defines the function name setColor, and color. Why do I have to declare it in the onClick function:
<button onClick={()=>setColor('Aquamarine')}>Aquamarine</button>

shouldn’t it be:

<button onClick={setColor('Aquamarine')}>Aquamarine</button>
  1. Why was the constant updated with the color function and not the new setColor function? Color is the existing color. setColor is the new color that is assigned. Shouldn’t we pass that as a parameter versus color?
 const divStyle = {backgroundColor: color};

shouldn’t it be:

 const divStyle = {backgroundColor: setColor};

Below is the code for the lesson

import React, { useState } from 'react';

export default function ColorPicker() {
  // call useState and assign its return values to `color` and `setColor`
 const [color, setColor] = useState()
 const divStyle = {backgroundColor: color};

  return (
    <div style={divStyle}>
      <p>The color is {color}</p>
      <button onClick={()=>setColor('Aquamarine')}>Aquamarine</button>
      <button onClick={()=>setColor('BlueViolet')}>BlueViolet</button>
      <button onClick={()=>setColor('Chartreuse')}>Chartreuse</button>
      <button onClick={()=>setColor('CornflowerBlue')}>CornflowerBlue</button>
    </div>
  );
}```
  1. No it shouldn’t! Because in the second example you CALLED setColor() function with ‘Aquamarine’ , not assign this function to onClick event listener. You’ll get infinite loop,

Calling the state setter signals to React that the component needs to re-render, so the whole function defining the component is called again.

→ call setColor(‘Aquamarine’) → re-render component call component func → call setColor(‘Aquamarine’) → re-render component call component func ->->->->->…
When you are assigning you use your function like variable with name setColor. But you have to put value as an argument to the function setColor() and not call this function=)). Use setColor call inside an inline callback function that doesn’t use any arguments. This arrow function calls the state setter function with the new value as an argument.
<button onClick={()=>setColor('Aquamarine')}>Aquamarine</button>

  1. setColor update color and then you use color in divStyle object. color is not a function, it’s a value.
  • color - the current color of this state
  • setColor - a function that we can use to update the color of this state
    In your example you try to assign function to the backgroundColor)) If you call this function const divStyle = {backgroundColor: setColor()}; I think you’ll get infinite loop.