handlesubmit = (event) => {
  event.preventDefault();
  console.log(this.clientimput.current.value);};
  

<form onSubmit={this.handlesubmit}>

   <input ref={this.clientimput} type="text" placeholder="ajouyer un souhait" />
   <button>Validation</button>
 </form>

state = {
  clients: [
    { id: 1, nom: "toto" },
    { id: 2, nom: "tutu" },
    { id: 3, nom: "titi" }
  ],
  nouvveauclient: "";
};