从JSON中的对象数组中只获取一个元素

Question

我怎样才能从JSON文件中获取名称.此外,代码完全适用于从"file.json"获取数据,即这不是问题.

JavaScript的:

var data = [];
function getName() {
  //what should I write here to get only name from the first object i.e. John
  //with this: data[0].name I am getting error!
}

var xhttp;
if(window.XMLHttpRequest)
  xhttp = new XMLHttpRequest();
else
  xhttp = new ActiveXObject("Microsoft.XMLHTTP");
    
xhttp.onreadystatechange = function() {
  if(xhttp.readyState == 4) {
    data = JSON.parse(xhttp.responseText);
    getName();
  }
}

xhttp.open("GET","file.json",true);
xhttp.send();

"file.json" - JSON:

[
  {
    "name":"John",
    "city":"London"
  },
  {
    "name":"Maria",
    "city":"Rome"
  }
]

Answer 1

通过函数传递变量数据

var data = [];
function getName(data) {
  return data[0].name;
}

var xhttp;
if(window.XMLHttpRequest)
  xhttp = new XMLHttpRequest();
else
  xhttp = new ActiveXObject("Microsoft.XMLHTTP");

xhttp.onreadystatechange = function() {
  if(xhttp.readyState == 4) {
    data = JSON.parse(xhttp.responseText);
    getName(data);
  }
}

xhttp.open("GET","file.json",true);
xhttp.send();

此外,如果要检索所有名称,可以执行以下操作:

function getName(data) {
  var names = [];
  for (var i = 0; i < data.length; i++) {
      names.push(data[i].name);
  }
  return names;
}

(数据是数组数据)

Answer 2

使用Array.prototype.map()来转换数组的项：

data.map(function(item) {
    return item.name
});