Why does one http req work then the other one doesnt

// this one works
var xhttp = new XMLHttpRequest()
xhttp.onload = function () {
  let data = this.responseText
  let jsonData = JSON.parse(data)
  let *** = jsonData[********].img
  document.getElementById("*******").src = ***
}
xhttp.open("GET", "https://**********************")
xhttp.send()

// this one's responseText is null
var x = new XMLHttpRequest()
var data
x.onload = function () {
  data = this.responseText
  let jsonData = JSON.parse(data)
  data = jsonDat
}
xhttp.open("GET", "https://*************************************")
xhttp.send()
for (var i = 0; i > data.length; i++) {
  a = data[i]
  if (a.****** == ******) {
    ********** = a.******
  }
}