Get which field changed on the event onChange

[eddyzhang1986]

Description

when the field value change,I just want to known which field i changed
how can i do?

Steps to Reproduce

1. when the field value change,I just want to known which field i changed
   how can i do?

[manahga]

I was able to accomplish this through the creation of a custom SchemaField component which acts as a wrapper to the original SchemaField and intercepts the onChange event of the underlying field. It then forwards the changed field value, along with the field name, to a callback function provided in the formContext of the form. I used the formContext as I couldn't find another way of passing a custom callback down to the custom SchemaField component.

import React from 'react';
import SchemaField from 'react-jsonschema-form/lib/components/fields/SchemaField';

const CustomSchemaField = function (props) {

    const customProps = {};

    //Only process if we are dealing with a field, not the parent object
    if (props.name) {

        const formContext = props.registry.formContext;        
        
        //Store the original onChange event provided to the SchemaField
        //as well as the name of the field
        const { onChange, name } = props;

        //Provide a new onChange event for the SchemaField
        customProps.onChange = function(formData) {

            //Call the custom handler provided in the formContext, if it exists,
            //with the field name and new value
            if (formContext && formContext.onFieldChange && 
                typeof formContext.onFieldChange === 'function') {

                formContext.onFieldChange(name, formData);
            }

            //Call the original onChange handler
            onChange(formData);
        };

    }

    return (
        <SchemaField {...props} {...customProps} />
    );
};

The above would be utilized like so:

class MyComponent extends React.Component {

    constructor(props) {
        super(props);
    }

    onFieldChange = (name, formData) => {
        //Handle individual field change here...
    }

    render() {
       const formContext = {
           onFieldChange: this.onFieldChange
       };
       return <Form ... fields={{ SchemaField: CustomSchemaField }} formContext={formContext} />
    }

}

There certainly may be an easier way...but this has worked for me.

[heath-freenome]

This was fixed in 5.x with #3173