Unnecessary DOM update for dynamic React elements - reactjs

Question

I have a React project that generates some DOM elements "dynamically" within JSX:
<div className='ui form'>
<h2 className="header">{subtype}</h2>
{
subtypes[subtype].fields.map((field) =>
<div className='field' key={field.name}>
<label>{field.label}</label>
<input name={field.name}
value={entity[field.name]}
onChange={onInputChange}/>
</div>
)
}
</div>
For a specific component, the generated input fields don't ever change during the life of the application (only their props change), so it is just a way to generate forms that are actually static.
So it is exactly equivalent to this "static" JSX:
<div className='ui form'>
<h2 className="header">{subtype}</h2>
<div className='field' key='field1'>
<label>Field 1</label>
<input name='field1'
value={entity['field1']}
onChange={onInputChange}/>
</div>
<div className='field' key='field2'>
<label>Field 2</label>
<input name='field2'
value={entity['field2']}
onChange={onInputChange}/>
</div>
</div>
If I used the first code snippet, then the HTML DOM elements get recreated on every change to state / props. If I use the second snippet, then the HTML appears to be unchanged and only the field values are updated (React can detect in the second instance that the virtual DOM elements are still the same, but not in the first instance)
Is there a way for me to create the "dynamic" virtual DOM in the first code example in a way that it can be cached and reused so that React sees it as being the same on each render?
Many thanks

Answer 1

Where is subtypes coming from? From what I understand you are receiving this in the component's props. If that is the case, you need to store this variable in this component's state. Then, you need to update it's state in it's componentWillReceiveProps lifecycle function.
The thing is, your component will only re-render when it's setState function is called. Hence, the components will not re-render when it's props change (after it has already been mounted).
class SimpleCom extends React.Component {
constructor(props) {
super(props);
this.state = {
subtypes: props.subtypes
}
}
componentWillReceiveProps(props) {
this.setState({
subtypes: props.subtypes
});
}
render() {
const subtypes = this.state.subtypes;
return (
<div className='ui form'>
<h2 className="header">{subtype}</h2>
{
subtypes[subtype].fields.map((field) =>
<div className='field' key={field.name}>
<label>{field.label}</label>
<input name={field.name}
value={entity[field.name]}
onChange={onInputChange}/>
</div>
)
}
</div>
);
}
}