[рони]

dima85,

const data = {
 "sdf":"1",
 "content":[
  {
   "sdf":"1",
   "test":"sdf"
  },
  {
   "123":"333"
  },
  {
   "sdfdsf":"33",
   "4524":"222"
  }
]}
const index = 2;
data.content.unshift(data.content.splice(index, 1)[0]);
console.log(data)