React will issue a warning in dev if you pass a non-object to the `style` prop on DOM element tags https://github.com/facebook/react/blob/85dcbf83/src/renderers/dom/shared/ReactDOMComponent.js#L204-L207 This should be easy enough to enforce for most cases with a linter rule. Bad: ``` jsx <div style="foo" /> ``` ``` jsx <div style={true} /> ``` ``` jsx const styles = true; <div style={styles} /> ``` Good: ``` jsx <div style={{ color: 'red' }} /> ``` ``` jsx const styles = { color: 'red' }; <div style={styles} /> ``` It would be even nicer if it validated that the values of the style object are all strings.