Using props in React style attribute

(I am using JSX with ES6 syntax)

This works:

render() {
  return (
    <div style={{ width: '95%' }}></div>
  )
}

This doesn't work: (why not?) Edit: It actually does work

render() {
  return (
    <div style={{ width: this.props.progress + '%' }}></div>
  )
}

Edit:

It works but the style value has to be a valid value else it will return the error.

I use the state to create the style object and clean out the property with a regular expression in the constructor, so it will not be error-ing again because of invalid values. Here is my solution:

import React, { Component, PropTypes } from 'react'

export default class ProgressBar extends Component {
  constructor(props) {
    super(props)
    let progress = +props.progress.replace(/[^0-9]/g, '') || 50
    this.state = {
      style: {
        width: progress + '%'
      }
    }
  }

  render() {
    return (
    ...
      <div className="progress-bar" role="progressbar" aria-valuenow={ this.state.progress } style={ this.state.style }></div>
    ...
    )
  }
}
ProgressBar.propTypes = {
  progress: PropTypes.string.isRequired
}