What are the effects of mutating event.target.value in React?

Tech QnA
1

We are building a custom input component.
Like, let’s say we wish to change the particular value from a string to a number. Here is the code snippet given below:
const CustomInputComponent = ({ onChange, …rest }) => {
const onChangeHandler = (event)=>{
// What are the consequences of doing this?
event.target.value = parseInt(event.target.value, 10);
onChange(event);
}
return
}
Just want to know what will be the consequences if we directly mutate the event.target.value like this?

2 Likes
2

Hey Roman,

There would be no consequences in terms of issues or errors in the code if you wanted to know that.

The only visible consequence of this would be user will only be able to enter integer in the input box and no characters, as you are parsing the user entered value as an Integer and setting it back in the input.

However, if the user input starts with a character then it would be set as “NaN”.

Hope this helps

Thanks

3

Got it! Thanks, Mudit for your response.

4

How can mutations to event.target.value impact the React component state?

1 Like
5

Hey Pulko! Welcome back again to our community.

Changes made to event.target.value may directly affect the state of a React component, particularly when controlled components are involved. Any changes to the input value should be reflected in the state and vice versa, as controlled components in React bind the value of form elements to the component state.

A straight modification to event.target.value without first updating the state could cause an out-of-synch between the rendered UI and the component. Unexpected behavior, problems with rendering, and difficulties keeping a single source of truth for the input value can result from this.

1 Like
6

Then, what are the potential side effects or performance considerations when directly modifying event.target.value in React?

1 Like
7

Directly changing event.target.value can cause several problems, including:

  1. Unpredictable State: Direct modifications might cause an out-of-synch state between the real DOM and the state of the React components since they circumvent React’s virtual DOM. This unpredictable nature could result in difficult-to-trace faults.

  2. Difficulties with Reconciliation: React depends on its virtual DOM for quick updates. Direct mutations could potentially affect performance by interfering with React’s ability to reconcile updates optimally.

  3. React components usually rerender when their state changes. This is known as component rendering. A stale user interface (UI) could result from the component not rendering as intended if event.target.value is changed without updating the state.

  4. Debugging Complexity: When changes are performed outside of the React state management framework, debugging is more difficult. It could result in code and goes against React’s declarative nature.

To guarantee consistency and predictable behavior, it is generally advised to avoid making direct changes to event.target.value in React and instead to update the state by the controlled component paradigm.