JSFiddle - React, Tailwind, and code Playground

JavaScript

var JSONtab=[{ _id: 'rWrEudqFWvsEB9q2T',
id: 10223,
createdAt: 'Sun Jun 05 2016 21:28:42 GMT+0200 (CEST)',
active: 'neutre',
ressource: 'Lavande',
auteur: 'scrom',
montant: 10000,
prixunite: 250,
total: 2500 },
{ _id: 'E3sdpToz3JqruGXsf',
id: 10899,
createdAt: 'Mon Jun 06 2016 08:25:02 GMT+0200 (CEST)',
active: 'neutre',
ressource: 'Lavande',
auteur: 'hoshis',
montant: 90000,
prixunite: 425,
total: 38250 },
{ _id: '8j7C8ZdmKmkgvQ9fk',
id: 10191,
createdAt: 'Mon Jun 06 2016 08:25:03 GMT+0200 (CEST)',
active: 'neutre',
ressource: 'Lavande',
auteur: 'mybad',
montant: 10000,
prixunite: 250,
total: 2500 },
{ _id: 'yrzqscuN5Kpowzifk',
id: 10185,
createdAt: 'Mon Jun 06 2016 08:25:01 GMT+0200 (CEST)',
active: 'neutre',
ressource: 'Lavande',
auteur: 'yoylo',
montant: 10000,
prixunite: 250,
total: 2500 }]

var Daystab={};
regday=/^.{15}/;
function PopulateDayTab(valeur, idx){ 
day=valeur.createdAt.match(regday)[0];
if(!Daystab[day]){Daystab[day]=[valeur];}
else{Daystab[day].push(valeur);}
}


JSONtab.forEach(PopulateDayTab);
for (myday in Daystab ){
   for( elt in Daystab[myday]){ 
console.log( myday+ ' => '+ Daystab[myday][elt]._id)
}
}