Should we add parenthesis when we call a function in props

Hi All,

I have a question, should we add parenthesis when we call a function in props? In below Button component, we add 2 props in it, both are function but one is with parenthesis another is without, so when should we add a parenthesis when we add props on component? More details in the link.

Thanks in advanced.

render() {
return (


<h1 className={this.isLight() ? ‘white’ : ‘black’}>
Your color is {this.formatColor(this.state.color)}!



);
}

https://drive.google.com/open?id=1X_3SdaWEbglVmZ-VAoxQd8CFb1UmJLpJ