Why does my export function get executed every time the TextInput changes?

Question

Why does my export function get executed every time the TextInput changes?

Hey there, here is my React and TypeScript code. I'm wondering why the console.log statement gets called every time my text field changes...

export default function TabOneScreen({
  navigation,
}) {
  
  const [out_1, set_out1] = useState('');
  const [out_2, set_out2] = useState('');
  const [main_device, setMain_dev] = useState('');
 
  


  console.log("This runs every time the text changes."); // It runs every time the text changes
 // Here I have some functions to initialize text input values and I don't want them to run every time


  return (
    <View style={styles.container}>
      <View style={{
      }}>


        <TextInput
          value={out_1}
          onChangeText={(username) => set_out1(username)}. 
        />

typescript react-native

Answer 1

Answer №1

Whenever the state changes, the function is triggered with the updated state. The primary lifecycle of a react component consists of: Mounting, Updating, Unmounting. When you initially render the element, it enters the mounting phase. Subsequently, when there are changes to the element's state or properties, it goes through an updating phase. Finally, when the element is removed, it undergoes unmounting. Each state update causes the entire component to be re-rendered using the same function. To ensure this function is only called once, it must be utilized during the mounting phase. Here's how:

useEffect(() => console.log("run every time .. on text changed ..") , [])

In the above code snippet, useEffect accepts two parameters - the function to run and the triggering state for running the function. With an empty array [], the function runs only during the mounting phase. If you want it to run based on another changing state, simply include that state in the array:

useEffect(() => console.log("run every time .. on out_1 changes ..") , [out_1])

This configuration ensures the function runs solely when the specified state (in this case, out_1) changes. For scenarios where data needs to be fetched from an API before the initial render and should not be repeated, utilizing the mounting phase with an empty array [] is essential for fetching this data.

Answer 2

Whenever the state changes, the function is triggered with the updated state. The primary lifecycle of a react component consists of: Mounting, Updating, Unmounting. When you initially render the element, it enters the mounting phase. Subsequently, when there are changes to the element's state or properties, it goes through an updating phase. Finally, when the element is removed, it undergoes unmounting. Each state update causes the entire component to be re-rendered using the same function. To ensure this function is only called once, it must be utilized during the mounting phase. Here's how:

useEffect(() => console.log("run every time .. on text changed ..") , [])

In the above code snippet, useEffect accepts two parameters - the function to run and the triggering state for running the function. With an empty array [], the function runs only during the mounting phase. If you want it to run based on another changing state, simply include that state in the array:

useEffect(() => console.log("run every time .. on out_1 changes ..") , [out_1])

This configuration ensures the function runs solely when the specified state (in this case, out_1) changes. For scenarios where data needs to be fetched from an API before the initial render and should not be repeated, utilizing the mounting phase with an empty array [] is essential for fetching this data.

Answer 3

Answer №2

Each instance the text is altered, it activates a function that modifies the state, leading to the component re-executing along with the console.log. To address this, encase your console.log or function within the useEffect hook as shown below:

useEffect(()=> {
console.log('...')
}, [])

Answer 4

Each instance the text is altered, it activates a function that modifies the state, leading to the component re-executing along with the console.log. To address this, encase your console.log or function within the useEffect hook as shown below:

useEffect(()=> {
console.log('...')
}, [])

Answer 5

Answer №3

Hey there, from my perspective it appears that React compares the old virtualDOM with the newly modified virtualDOM. So, when you use setState, you're essentially triggering a change in the component's state. Once this change occurs, console.log identifies it and visually reflects it on the screen.

Answer 6

Hey there, from my perspective it appears that React compares the old virtualDOM with the newly modified virtualDOM. So, when you use setState, you're essentially triggering a change in the component's state. Once this change occurs, console.log identifies it and visually reflects it on the screen.

Answer 7

Answer №4

Updating the text inside an input field triggers a state change.

onChangeText={(username) => set_out1(username)}

Once the state changes, the render method is called, causing the component to compare its current DOM with the previous one and re-render if necessary.

To avoid excessive re-renders, you can utilize lifecycle methods, conditional statements, or a library like Formik.

Answer 8

Updating the text inside an input field triggers a state change.

onChangeText={(username) => set_out1(username)}

Once the state changes, the render method is called, causing the component to compare its current DOM with the previous one and re-render if necessary.

To avoid excessive re-renders, you can utilize lifecycle methods, conditional statements, or a library like Formik.

Why does my export function get executed every time the TextInput changes?

Answer №1

Answer №2

Answer №3

Answer №4

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