How to invalidate a TextField in Material UI

As of 0.20.1 you can helperText and error props

<TextField 
    hintText="Phone"
    error ={this.state.errorText.length === 0 ? false : true }
    floatingLabelText="Phone"
    name="phone"
    helperText={this.state.errorText}
    onChange={this.onChange.bind(this)}/>