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Changing an Uncontrolled Input to Controlled Error in React

monknomo profile image Gunnar Gissel Updated on ・2 min read

React wants form inputs and the like to keep their state inside React, inside of inside the input. This style is called a "controlled input". They also offer "uncontrolled input" where the input manages its own state.

React apparently does not like inputs switching from controlled to uncontrolled. I was developing a form with the docs open next to my editor and I kept getting a Warning: CustomInput is changing an uncontrolled input of type text to be controlled. Input elements should not switch from uncontrolled to controlled (or vice versa). Decide between using a controlled or uncontrolled input element for the lifetime of the component. More info:https://fb.me/react-controlled-components

As far as I could tell, my input was set up to always be controlled. I changed javascript around and googled for quite some time before realization set in

I was Switching a Form Value from '' to null

This is apparently a no-no in React's controlled component land. My initial state set up had all empty strings, and the only subsequent state manipulation was to get data from webservices. The webservices I'm working with return a fairly faithful representation of data from a database - nulls and all.

I solved it by converting my state variable to const in the render method - with a twist:

const nullable = this.state.nullable == null ? '' : this.state.nullable;

A little sprinkling of last minute converters and all is well.

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Thank you Sebastian Dooris for the sprinkles

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Gunnar Gissel

@monknomo

Saving fish by writing code! Applications developer in fisheries, specializing in webapps and moving 'enterprise-y' legacy systems to modern agile systems - Email or tweet me if you want to talk!

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