how can write code to store uniqe value in firebase by using angular and ionic

Question

we want store uniqe incident id for each incident stored in firebase

this on server page

add_incident(pro) {

console.log(pro)

return this.afs.collection('Incident').add(pro);}

this on addincudent.ts

async savecase(){

let pro = {

incidentid:this.incidentid,

civilid:this.civilid,

incidentdate:this.incidentdate,

};

 if(this.incidentid && this.civilid && this.incidentdate)

{

  const loading= await this.loadingCtrl.create({

    message:"loading---",

    spinner:"crescent",

    showBackdrop:true

  });

  loading.present();    

this.auth.add_incident(pro).then(resp => {

  this.incidentid = "";

  this.civilid = "";

  this.incidentdate = "";

  console.log(resp);

  loading.dismiss();

  this.toast('save Success!','success'); this.router.navigate(['/incidentpage']);

})

  .catch(error => {

    console.log(error);

  });

}