JSFiddle - React, Tailwind, and code Playground

JavaScript

var data = {
  "obj": [{
    "name": "John",
    "age": "10",
    "Alias": "Person",
    "where": [{
      "City1": "foo",
      "City2": "foo2"
    }]
  }, {
    "name": "Mike",
    "age": "11",
    "Alias": "Person2",
    "where": [{
      "City1": "test1",
      "City2": "test2"
    }]
  }]
}

var temp = []
var final = data.obj.filter((x, i) => {
  //console.log(x)
  console.log(i)
  if (x.age.length == 0) {
    return false
  } else {
    if (temp.indexOf(x.Alias) > -1) {
      return false
    } else {
      temp.push(x.Alias)
      return true
    }
  }
})

console.log(final.length == data.obj.length ? "Valid" : "Not valid JSON")