how to get value of checkbox in react js

I am trying to retrieve the check value of my checkbox but i get null value this is my code

<form onSubmit={this.onSubmit}>
<fieldset>
<legend>RFX/RFP:</legend>
<div className="form-check">
  <input type="checkbox" className="form-check-input" onChange={this.onChange}  value={this.state.rfx} name="rfx" id="rfx" />
  <label className="form-check-label"  name="rfx">RFX</label>
  &nbsp; &nbsp; &nbsp; &nbsp;

  <input type="checkbox" className="form-check-input" onChange={this.onChange}  value={this.state.rfp}  name="rfp" id="rfp"  />
  
  <label className="form-check-label" >RFP</label>
  &nbsp; &nbsp; &nbsp; &nbsp;

  <input type="checkbox" className="form-check-input" onChange={this.onChange}  value={this.state.rfp_x}  name="rfp(x)" id="rfp(x)"/>
  <label className="form-check-label" >RFP(X)</label>
  &nbsp; &nbsp; &nbsp; &nbsp;


  <input type="checkbox" className="form-check-input"  onChange={this.onChange}name="all" id="all" />
  <label className="form-check-label"  name="all" id="all">ALL</label>
</div>
</form>

and my methods :

constructor(props){
    super(props)
    this.state={
      rfp:"",
      rfx:"",
      rfp_x:"",
      all:"",
    
 
    }
    this.onChange =  this.onChange.bind(this);
    this.onSubmit = this.onSubmit.bind(this);
   }
  onChange(e){
    this.setState({[e.target.name] : e.target.value});}
  onSubmit(e){
    e.preventDefault();
    const FilterRegion={
  
      rfx:this.state.rfx,
      rfp:this.state.rfp,
      rfp_x:this.state.rfp_x,
      all:this.state.all,
    }
    console.log(FilterRegion)
   }

and the screen when i submit my form :

https://gyazo.com/32a24813545ebf7d3a48b72be724a76f

please I try to solve my problem and display the value or the name of my check box! what do I have to do