I usually use it when initializing

constructor(props) {
  super(props);
  // ...
  this.stream = null;
  this.video = null;
  // ...
}

what is the difference between the above two initializations?

when this.xxx appears in my impression, this xxx should be a method ( < Component onClick= {this.doSth} / > )

his this.stream = null; can I use it directly? For example,

modify this.stream=100 or

value if (this.stream = 100) / /. like this?